Delta-5 desaturase and uses thereof

ABSTRACT

The subject invention relates to the identification of genes involved in the desaturation of polyunsaturated fatty acids at carbon 5 (i.e., “Δ5-desaturase”) and at carbon 6 (i.e., “Δ6-desaturase”) and to uses thereof. In particular, Δ5-desaturase may be utilized, for example, in the conversion of dihomo-γ-linolenic acid (DGLA) to arachidonic acid (AA) and in the conversion of 20:4n-3 to eicosapentaenoic acid (EPA). Delta-6 desaturase may be used, for example, in the conversion of linoleic (LA) to γ-linolenic acid (GLA). AA or polyunsaturated fatty acids produced therefrom may be added to pharmaceutical compositions, nutritional compositions, animal feeds, as well as other products such as cosmetics.

This application is a divisional of U.S. patent application Ser. No.11/800,631, filed on May 7, 2007, which is a divisional of U.S. patentapplication Ser. No. 10/431,952, filed on May 8, 2003, now U.S. Pat. No.7,241,619, which is a divisional of U.S. patent application Ser. No.09/769,863, filed on Jan. 25, 2001, now U.S. Pat. No. 6,635,451, all ofwhich are incorporated in their entirety by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The subject invention relates to the identification and isolation ofgenes that encodes enzymes (i.e., Thraustochytrium aureum β5-desaturase,Saprolegnia diclina Δ5-desaturase and Saprolegnia diclina Δ6-desaturase)involved in the synthesis of polyunsaturated fatty acids and to usesthereof. In particular, Δ5-desaturase catalyzes the conversion of, forexample, dihomo-γ-linolenic acid (DGLA) to arachidonic acid (AA) and(n-3)-eicosatetraenoic acid (20:4n-3) to eicosapentaenoic acid(20:5n-3). Delta-6 desaturase catalyzes the conversion of, for example,α-linolenic acid (ALA) to stearidonic acid (STA). The converted productsmay then be utilized as substrates in the production of otherpolyunsaturated fatty acids (PUFAs). The product or otherpolyunsaturated fatty acids may be added to pharmaceutical compositions,nutritional composition, animal feeds as well as other products such ascosmetics.

2. Background Information

Desaturases are critical in the production of long-chain polyunsaturatedfatty acids that have many important functions. For example,polyunsaturated fatty acids (PUFAs) are important components of theplasma membrane of a cell, where they are found in the form ofphospholipids. They also serve as precursors to mammalian prostacyclins,eicosanoids, leukotrienes and prostaglandins. Additionally, PUFAs arenecessary for the proper development of the developing infant brain aswell as for tissue formation and repair. In view of the biologicalsignificance of PUFAs, attempts are being made to produce them, as wellas intermediates leading to their production, in an efficient manner.

A number of enzymes are involved in PUFA biosynthesis in addition toΔ5-desaturase and Δ6-desaturase. For example, elongase (elo) catalyzesthe conversion of γ-linolenic acid (GLA) to dihomo-γ-linolenic acid(DGLA) and of stearidonic acid (18:4n-3) to (n-3)-eicosatetraenoic acid(20:4n-3). Linoleic acid (LA, 18:2-Δ9,12 or 18:2n-6) is produced fromoleic acid (18:1-Δ9) by a Δ12-desaturase. GLA (18:3-Δ6,9,12) is producedfrom linoleic acid by a Δ6-desaturase.

It must be noted that animals cannot desaturate beyond the Δ9 positionand therefore cannot convert oleic acid into linoleic acid. Likewise,α-linolenic acid (ALA, 18:3-Δ9,12,15) cannot be synthesized by mammals.However, α-linolenic acid can be converted to stearidonic acid (STA,18:4-Δ6,9,12,15) by a Δ6-desaturase (see PCT publication WO 96/13591 andThe Faseb Journal, Abstracts, Part I, Abstract 3093, page Δ532(Experimental Biology 98, San Francisco, Calif., Apr. 18-22, 1998); seealso U.S. Pat. No. 5,552,306), followed by elongation to(n-3)-eicosatetraenoic acid (20:4-Δ8,11,14,17) in mammals and algae.This polyunsaturated fatty acid (i.e., 20:4-Δ8,11,14,17) can then beconverted to eicosapentaenoic acid (EPA, 20:5-Δ5,8,11,14,17) by aΔ5-desaturase, such as that of the present invention. Other eukaryotes,including fungi and plants, have enzymes which desaturate at carbon 12(see PCT publication WO 94/11516 and U.S. Pat. No. 5,443,974) and carbon15 (see PCT publication WO 93/11245). The major polyunsaturated fattyacids of animals therefore are either derived from diet and/or fromdesaturation and elongation of linoleic acid or α-linolenic acid. Inview of these difficulties, it is of significant interest to isolategenes involved in PUFA synthesis from species that naturally producethese fatty acids and to express these genes in a microbial, plant, oranimal system which can be altered to provide production of commercialquantities of one or more PUFAs.

One of the most important long chain PUFAs, noted above, is arachidonicacid (AA). AA is found in filamentous fungi and can also be purifiedfrom mammalian tissues including the liver and adrenal glands. As notedabove, AA production from dihomo-γ-linolenic acid is catalyzed by aΔ5-desaturase. EPA is another important long-chain PUFA. EPA is found infungi and also in marine oils. As noted above, EPA is produced from(n-3)-eicosatetraenoic acid and is catalyzed by a Δ5-desaturase. In viewof the above discussion, there is a definite need for the Δ5-desaturaseand Δ6-desaturase enzymes, the respective genes encoding these enzymes,as well as recombinant methods of producing these enzymes. Additionally,a need exists for oils containing levels of PUFAs beyond those naturallypresent as well as those enriched in novel PUFAs. Such oils can only bemade by isolation and expression of the Δ5-desaturase and Δ6-desaturasegenes.

All U.S. patents and publications referred to herein are herebyincorporated in their entirety by reference.

SUMMARY OF THE INVENTION

The present invention includes an isolated nucleotide sequencecorresponding to or complementary to at least about 50% of thenucleotide sequence comprising SEQ ID NO:13 (FIG. 2), SEQ ID NO:19 (FIG.4) or SEQ ID NO:28 (FIG. 6).

The isolated nucleotide sequence may be represented by SEQ ID NO:13, SEQID NO:19 or SEQ ID NO:28. These sequences may encode a functionallyactive desaturase which utilizes a polyunsaturated fatty acid as asubstrate. The sequences may be derived from, for example, a fungus suchas Saprolegnia diclina (SEQ ID NO:13 and SEQ ID NO:19) andThraustochytrium aureum (SEQ ID NO:28).

The present invention also includes purified proteins (SEQ ID NO:14(FIG. 3), SEQ ID NO:20 (FIG. 5) and SEQ ID NO:29 (FIG. 7)) encoded bythe nucleotide sequences referred to above.

Additionally, the present invention includes a purified polypeptidewhich desaturates polyunsaturated fatty acids at carbon 5 or carbon 6and has at least about 50% amino acid similarity to the amino acidsequence of the purified proteins referred to directly above (i.e., SEQID NO:14, SEQ ID NO:20 or SEQ ID NO:29).

Furthermore, the present invention also encompasses a method ofproducing a desaturase (i.e., Δ5 or Δ6). This method comprises the stepsof: a) isolating the nucleotide sequence comprising SEQ ID NO:19, SEQ IDNO:28, or SEQ ID NO:13, as appropriate; b) constructing a vectorcomprising: i) the isolated nucleotide sequence operably linked to ii) apromoter; and c) introducing the vector into a host cell under time andconditions sufficient for expression of the Δ5-desaturase orΔ6-desaturase. The host cell may be, for example, a eukaryotic cell or aprokaryotic cell. In particular, the prokaryotic cell may be, forexample, E. coli, cyanobacteria or B. subtilis. The eukaryotic cell maybe, for example, a mammalian cell, an insect cell, a plant cell or afungal cell (e.g., a yeast cell such as Saccharomyces cerevisiae,Saccharomyces carlsbergensis, Candida spp., Lipomyces starkey, Yarrowialipolytica, Kluvveromyces spp., Hansenula spp., Trichoderma spp. orPichia spp.).

Additionally, the present invention also encompasses a vectorcomprising: a) a nucleotide sequence as represented by SEQ ID NO:13, SEQID NO:19 or SEQ ID NO:28 operably linked to b) a promoter. The inventionalso includes a host cell comprising this vector. The host cell may be,for example, a eukaryotic cell or a prokaryotic cell. Suitableeukaryotic cells and prokaryotic cells are as defined above.

Moreover, the present invention also includes a plant cell, plant orplant tissue comprising the above vector, wherein expression of thenucleotide sequence of the vector results in production of apolyunsaturated fatty acid by the plant cell, plant or plant tissue. Thepolyunsaturated fatty acid may be, for example, selected from the groupconsisting of AA, EPA, GLA or STA, depending upon whether the nucleotidesequence encodes a Δ5- or Δ6-desaturase. The invention also includes oneor more plant oils or acids expressed by the above plant cell, plant orplant tissue.

Additionally, the present invention also encompasses a transgenic plantcomprising the above vector, wherein expression of the nucleotidesequence of the vector results in production of a polyunsaturated fattyacid in seeds of the transgenic plant.

Also, the invention includes a mammalian cell comprising the abovevector wherein expression of the nucleotide sequence of the vectorresults in production of altered levels of AA, EPA, GLA and/or STA whenthe cell is grown in a culture media comprising a fatty acid selectedfrom the group consisting of, for example, LA, ALA, DGLA and ETA.

It should also be noted that the present invention encompasses atransgenic, non-human mammal whose genome comprises a DNA sequenceencoding a Δ5-desaturase or a Δ6-desaturase, operably linked to apromoter. The DNA sequence may be represented by SEQ ID NO:13 (Δ6), SEQID NO:19 (Δ5) or SEQ ID NO:28 (Δ5). Additionally, the present inventionincludes a fluid (e.g., milk) produced by the transgenic, non-humanmammal wherein the fluid comprises a detectable level of at leastΔ5-desaturase or at least Δ6-desaturase, as appropriate.

Additionally, the present invention includes a method (i.e., “first”method) for producing a polyunsaturated fatty acid comprising the stepsof: a) isolating the nucleotide sequence represented by SEQ ID NO:19 orSEQ ID NO:28; b) constructing a vector comprising the isolatednucleotide sequence; c) introducing the vector into a host cell undertime and conditions sufficient for expression of Δ5-desaturase enzyme;and d) exposing the expressed human Δ5-desaturase enzyme to a substratepolyunsaturated fatty acid in order to convert the substrate to aproduct polyunsaturated fatty acid. The substrate polyunsaturated fattyacid may be, for example, DGLA or 20:4n-3 and the productpolyunsaturated fatty acid may be, for example, AA or EPA, respectively.This method may further comprise the step of exposing the productpolyunsaturated fatty acid to an elongase in order to convert theproduct polyunsaturated fatty acid to another polyunsaturated fatty acid(i.e., “second” method). In this method containing the additional step(i.e., “second” method), the product polyunsaturated fatty acid may be,for example, AA or EPA, and the “another” polyunsaturated fatty acid maybe adrenic acid or (n-3)-docosapentaenoic acid, respectively. The methodcontaining the additional step may further comprise a step of exposingthe another polyunsaturated fatty acid to an additional desaturase inorder to convert the another polyunsaturated fatty acid to a finalpolyunsaturated fatty acid (i.e., “third” method). The finalpolyunsaturated fatty acid may be, for example, (n-6)-docosapentaenoicacid or docosahexaenoic (DHA) acid.

Additionally, the present invention includes a method for producing apolyunsaturated fatty acid comprising the steps of: a) isolating thenucleotide sequence represented by SEQ ID NO:13; b) constructing avector comprising the isolated nucleotide sequence; c) introducing thevector into a host cell under time and conditions sufficient forexpression of Δ6-desaturase enzyme; and d) exposing the expressedΔ6-desaturase enzyme to a substrate polyunsaturated fatty acid in orderto convert the substrate to a product polyunsaturated fatty acid. Thesubstrate polyunsaturated fatty acid may be, for example, LA or ALA, andthe product polyunsaturated fatty acid may be, for example, GLA or STA,respectively. This method may further comprise the step of exposing theproduct polyunsaturated fatty acid to an elongase in order to convertthe product polyunsaturated fatty acid to another polyunsaturated fattyacid. In this method containing the additional step, the productpolyunsaturated fatty acid may be, for example, GLA or STA, and the“another” polyunsaturated fatty acid may be DGLA or eicosatetraenoicacid (ETA), respectively. The method containing the additional step mayfurther comprise a step of exposing the another polyunsaturated fattyacid to an additional desaturase in order to convert the anotherpolyunsaturated fatty acid to a final polyunsaturated fatty acid. Thefinal polyunsaturated fatty acid may be, for example, AA or EPA.

The present invention also encompasses a nutritional compositioncomprising at least one polyunsaturated fatty acid selected from thegroup consisting of the product polyunsaturated fatty acid producedaccording to the methods described above, the another polyunsaturatedfatty acid produced according to the methods described above, and thefinal polyunsaturated fatty acid produced according to the methodsdescribed above. The product polyunsaturated fatty acid may be, forexample, AA, EPA, GLA or STA, depending upon whether one is using a Δ5-or Δ6-desaturase nucleotide sequence. The another polyunsaturated fattyacid may be, for example, adrenic acid, (n-3)-docosapentaenoic acid,DGLA and EPA, again depending upon whether one is using a Δ5- orΔ6-desaturase nucleotide sequence. The final polyunsaturated fatty acidmay be, for example, (n-6)-docosapentaenoic acid, DHA, AA or EPA, again,depending upon whether one is using a Δ5- or Δ6-desaturase nucleotidesequence.

The present invention also includes a pharmaceutical compositioncomprising 1) at least one PUFA selected from the group consisting ofthe product PUFA produced according to the methods described above, theanother PUFA produced according to the methods described above, or thefinal PUFA produced according to the methods described above and 2) apharmaceutically acceptable carrier.

Additionally, the present invention encompasses an animal feed orcosmetic comprising at least one PUFA selected from the group consistingof the product PUFA produced according to the methods described above,the another PUFA produced according to the methods described above andthe final PUFA produced according to one of the methods described above.These PUFA have been listed above and are exemplified in FIG. 1.

Additionally, the present invention encompasses a method of preventingor treating a condition caused by insufficient intake of polyunsaturatedfatty acids comprising administering to the patient the nutritionalcomposition above in an amount sufficient to effect prevention ortreatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the fatty acid biosynthetic pathway and the roles ofΔ5-desaturase and Δ6-desaturase in this pathway.

FIG. 2 illustrates the nucleotide sequence encoding Δ6-desaturase ofSaprolegnia diclina (ATCC 56851) (SEQ ID NO:13).

FIG. 3 illustrates the amino acid sequence of Δ6-desaturase ofSaprolegnia diclina (ATCC 56851) (SEQ ID NO:14).

FIG. 4 illustrates the nucleotide sequence encoding Δ5-desaturase ofSaprolegnia diclina (ATCC 56851) (SEQ ID NO:19).

FIG. 5 illustrates the amino acid sequence of Δ5-desaturase ofSaprolegnia diclina (ATCC 56851) (SEQ ID NO:20).

FIG. 6 illustrates the nucleotide sequence encoding Δ5-desaturase ofThraustochytrium aureum (ATCC 34304) (SEQ ID NO:28).

FIG. 7 illustrates the amino acid sequence of Δ5-desaturase ofThraustochytrium aureum (ATCC 34304) (SEQ ID NO:29).

DETAILED DESCRIPTION OF THE INVENTION

The subject invention relates to the nucleotide and translated aminoacid sequences of the Δ5-desaturase gene derived from Saprolegniadiclina, the Δ6-desaturase gene derived from Saprolegnia diclina, andthe Δ5-desaturase gene derived from Thraustochytrium aureum.Furthermore, the subject invention also includes uses of these genes andof the enzymes encoded by these genes. For example, the genes andcorresponding enzymes may be used in the production of polyunsaturatedfatty acids such as, for instance, arachidonic acid, eicosapentaenoicacid, and/or adrenic acid which may be added to pharmaceuticalcompositions, nutritional compositions and to other valuable products.

The Δ5-Desaturase Genes, the Δ6-Desaturase Gene, and Enzymes EncodedThereby

As noted above, the enzymes encoded by the Δ5-desaturase genes andΔ6-desaturase gene of the present invention are essential in theproduction of highly unsaturated polyunsaturated fatty acids having alength greater than 20 and 18 carbons, respectively. The nucleotidesequence of the isolated Thraustochytrium aureum Δ5-desaturase gene isshown in FIG. 6, and the amino acid sequence of the correspondingpurified protein is shown in FIG. 7. The nucleotide sequence of theisolated Saprolegnia diclina Δ5-desaturase gene is shown in FIG. 4, andthe amino acid sequence of the corresponding purified protein is shownin FIG. 5. Finally, the nucleotide sequence of the isolated Saprolegniadiclina Δ6-desaturase gene is shown in FIG. 2, and the amino acidsequence of the corresponding purified protein is shown in FIG. 3.

As an example of the importance of the genes of the present invention,the isolated Δ5-desaturase genes convert DGLA to AA or converteicosatetraenoic acid to EPA. AA, for example, cannot be synthesizedwithout the Δ5-desaturase genes and enzymes encoded thereby. Theisolated Δ6-desaturase gene of the present invention converts, forexample, linoleic acid (18:2n-6) to γ-linoleic acid (GLA) andα-linolenic acid (GLA) to stearidonic acid (STA).

It should be noted that the present invention also encompassesnucleotide sequences (and the corresponding encoded proteins) havingsequences corresponding to or complementary to at least about 50%,preferably at least about 60%, and more preferably at least about 70% ofthe nucleotides in sequence to SEQ ID NO:19 (i.e., the nucleotidesequence of the β5-desaturase gene of Saprolegnia diclina), SEQ ID NO:13(i.e., the nucleotide sequence of the Δ6-desaturase gene ofThraustochyrium aureum) or SEQ ID NO:28 (i.e., the nucleotide sequenceof the Δ5-desaturase gene of Thraustochytrium aureum) described herein.Such sequences may be derived from human sources as well as othernon-human sources (e.g., C. elegans or mouse). Furthermore, the presentinvention also encompasses fragments and derivatives of the nucleotidesequences of the present invention (i.e., SEQ ID NO:13, SEQ ID NO:19 andSEQ ID NO:28), as well as of the sequences derived from other sources,and having the above-described complementarity or correspondence.Functional equivalents of the above-sequences (i.e., sequences havingΔ5-desaturase activity or Δ6-desaturase activity, as appropriate) arealso encompassed by the present invention.

The invention also includes a purified polypeptide which desaturatespolyunsaturated fatty acids at the carbon 5 position or carbon 6position and has at least about 50% amino acid similarity, preferably atleast about 60% similarity, and more preferably at least about 70%similarity to the amino acid sequences (i.e., SEQ ID NO:14 (shown inFIG. 3), SEQ ID NO:20 (shown in FIG. 5) and SEQ ID NO:29 (shown in FIG.7)) of the above-noted proteins which are, in turn, encoded by theabove-described nucleotide sequences.

The present invention also encompasses an isolated nucleotide sequencewhich encodes PUFA desaturase activity and that is hybridizable, undermoderately stringent conditions, to a nucleic acid having a nucleotidesequence corresponding to or complementary to the nucleotide sequencecomprising or represented by SEQ ID NO:13 (shown in FIG. 2), SEQ IDNO:19 (shown in FIG. 4), or SEQ ID NO:28 (shown in FIG. 6). A nucleicacid molecule is “hybridizable” to another nucleic acid molecule when asingle-stranded form of the nucleic acid molecule can anneal to theother nucleic acid molecule under the appropriate conditions oftemperature and ionic strength (see Sambrook et al., “Molecular Cloning:A Laboratory Manual, Second Edition (1989), Cold Spring HarborLaboratory Press, Cold Spring Harbor, N.Y.)). The conditions oftemperature and ionic strength determine the “stringency” of thehybridization. “Hybridization” requires that two nucleic acids containcomplementary sequences. However, depending on the stringency of thehybridization, mismatches between bases may occur. The appropriatestringency for hybridizing nucleic acids depends on the length of thenucleic acids and the degree of complementation. Such variables are wellknown in the art. More specifically, the greater the degree ofsimilarity or homology between two nucleotide sequences, the greater thevalue of Tm for hybrids of nucleic acids having those sequences. Forhybrids of greater than 100 nucleotides in length, equations forcalculating Tm have been derived (see Sambrook et al., supra). Forhybridization with shorter nucleic acids, the position of mismatchesbecomes more important, and the length of the oligonucleotide determinesits specificity (see Sambrook et al., supra).

Production of the Two Δ5-Desaturase Enzymes and the Δ6-Desaturase Enzyme

Once the gene encoding any one of the desaturase enzymes has beenisolated, it may then be introduced into either a prokaryotic oreukaryotic host cell through the use of a vector or construct. Thevector, for example, a bacteriophage, cosmid or plasmid, may comprisethe nucleotide sequence encoding either of the Δ5-desaturase enzymes, orthe Δ6-desaturase enzyme, as well as any promoter which is functional inthe host cell and is able to elicit expression of the desaturase encodedby the nucleotide sequence. The promoter is in operable association withor operably linked to the nucleotide sequence. (A promoter is said to be“operably linked” with a coding sequence if the promoter affectstranscription or expression of the coding sequence.) Suitable promotersinclude, for example, those from genes encoding alcohol dehydrogenase,glyceraldehyde-3-phosphate dehydrogenase, phosphoglucoisomerase,phosphoglycerate kinase, acid phosphatase, T7, TPI, lactase,metallothionein, cytomegalovirus immediate early, whey acidic protein,glucoamylase, and promoters activated in the presence of galactose, forexample, GAL1 and GAL10. Additionally, nucleotide sequences which encodeother proteins, oligosaccharides, lipids, etc. may also be includedwithin the vector as well as other regulatory sequences such as apolyadenylation signal (e.g., the poly-A signal of SV-40T-antigen,ovalalbumin or bovine growth hormone). The choice of sequences presentin the construct is dependent upon the desired expression products aswell as the nature of the host cell.

As noted above, once the vector has been constructed, it may then beintroduced into the host cell of choice by methods known to those ofordinary skill in the art including, for example, transfection,transformation and electroporation (see Molecular Cloning: A LaboratoryManual, 2^(nd) ed., vol. 1-3, ed. Sambrook et al., Cold Spring HarborLaboratory Press (1989)). The host cell is then cultured under suitableconditions permitting expression of the genes leading to the productionof the desired PUFA, which is then recovered and purified.

Examples of suitable prokaryotic host cells include, for example,bacteria such as Escherichia coli, Bacillus subtilis as well ascyanobacteria such as Spirulina spp. (i.e., blue-green algae). Examplesof suitable eukaryotic host cells include, for example, mammalian cells,plant cells, yeast cells such as Saccharomyces cerevisiae, Saccharomycescarlsbergensis, Lipomyces starkey, Candida spp. such as Yarrowia(Candida) lipolytica, Kluyveromyces spp., Pichia spp., Trichoderma spp.or Hansenula spp., or fungal cells such as filamentous fungal cells, forexample, Aspergillus, Neurospora and Penicillium. Preferably,Saccharomyces cerevisiae (baker's yeast) cells are utilized.

Expression in a host cell can be accomplished in a transient or stablefashion. Transient expression can occur from introduced constructs whichcontain expression signals functional in the host cell, but whichconstructs do not replicate and rarely integrate in the host cell, orwhere the host cell is not proliferating. Transient expression also canbe accomplished by inducing the activity of a regulatable promoteroperably linked to the gene of interest, although such inducible systemsfrequently exhibit a low basal level of expression. Stable expressioncan be achieved by introduction of a construct that can integrate intothe host genome or that autonomously replicates in the host cell. Stableexpression of the gene of interest can be selected for through the useof a selectable marker located on or transfected with the expressionconstruct, followed by selection for cells expressing the marker. Whenstable expression results from integration, the site of the construct'sintegration can occur randomly within the host genome or can be targetedthrough the use of constructs containing regions of homology with thehost genome sufficient to target recombination with the host locus.Where constructs are targeted to an endogenous locus, all or some of thetranscriptional and translational regulatory regions can be provided bythe endogenous locus.

A transgenic mammal may also be used in order to express the enzyme(s)of interest (i.e., either of the two Δ5-desaturases, the Δ6-desaturase,or a combination thereof), and ultimately the PUFA(s) of interest. Morespecifically, once the above-described construct is created, it may beinserted into the pronucleus of an embryo. The embryo may then beimplanted into a recipient female. Alternatively, a nuclear transfermethod could also be utilized (Schnieke et al., Science 278:2130-2133(1997)). Gestation and birth are then permitted (see, e.g., U.S. Pat.No. 5,750,176 and U.S. Pat. No. 5,700,671). Milk, tissue or other fluidsamples from the offspring should then contain altered levels of PUFAs,as compared to the levels normally found in the non-transgenic animal.Subsequent generations may be monitored for production of the altered orenhanced levels of PUFAs and thus incorporation of the gene encoding thedesired desaturase enzyme into their genomes. The mammal utilized as thehost may be selected from the group consisting of, for example, a mouse,a rat, a rabbit, a pig, a goat, a sheep, a horse and a cow. However, anymammal may be used provided it has the ability to incorporate DNAencoding the enzyme of interest into its genome.

For expression of a desaturase polypeptide, functional transcriptionaland translational initiation and termination regions are operably linkedto the DNA encoding the desaturase polypeptide. Transcriptional andtranslational initiation and termination regions are derived from avariety of nonexclusive sources, including the DNA to be expressed,genes known or suspected to be capable of expression in the desiredsystem, expression vectors, chemical synthesis, or from an endogenouslocus in a host cell. Expression in a plant tissue and/or plant partpresents certain efficiencies, particularly where the tissue or part isone which is harvested early, such as seed, leaves, fruits, flowers,roots, etc. Expression can be targeted to that location with the plantby utilizing specific regulatory sequence such as those of U.S. Pat.Nos. 5,463,174, 4,943,674, 5,106,739, 5,175,095, 5,420,034, 5,188,958,and 5,589,379. Alternatively, the expressed protein can be an enzymewhich produces a product which may be incorporated, either directly orupon further modifications, into a fluid fraction from the host plant.Expression of a desaturase gene, or antisense desaturase transcripts,can alter the levels of specific PUFAs, or derivatives thereof, found inplant parts and/or plant tissues. The desaturase polypeptide codingregion may be expressed either by itself or with other genes, in orderto produce tissues and/or plant parts containing higher proportions ofdesired PUFAs or in which the PUFA composition more closely resemblesthat of human breast milk (Prieto et al., PCT publication WO 95/24494).The termination region may be derived from the 3′ region of the genefrom which the initiation region was obtained or from a different gene.A large number of termination regions are known to and have been foundto be satisfactory in a variety of hosts from the same and differentgenera and species. The termination region usually is selected as amatter of convenience rather than because of any particular property.

As noted above, a plant (e.g., Glycine max (soybean) or Brassica napus(canola)) or plant tissue may also be utilized as a host or host cell,respectively, for expression of the desaturase enzyme which may, inturn, be utilized in the production of polyunsaturated fatty acids. Morespecifically, desired PUFAS can be expressed in seed. Methods ofisolating seed oils are known in the art. Thus, in addition to providinga source for PUFAs, seed oil components may be manipulated through theexpression of the desaturase gene, as well as perhaps other desaturasegenes and elongase genes, in order to provide seed oils that can beadded to nutritional compositions, pharmaceutical compositions, animalfeeds and cosmetics. Once again, a vector which comprises a DNA sequenceencoding the desaturase operably linked to a promoter, will beintroduced into the plant tissue or plant for a time and underconditions sufficient for expression of the desaturase gene. The vectormay also comprise one or more genes that encode other enzymes, forexample, Δ4-desaturase, elongase, Δ12-desaturase, Δ15-desaturase,Δ17-desaturase, and/or Δ19-desaturase. The plant tissue or plant mayproduce the relevant substrate (e.g., DGLA (in the case ofΔ5-desaturase), ALA (in the case of Δ6-desaturase), etc.) upon which theenzymes act or a vector encoding enzymes which produce such substratesmay be introduced into the plant tissue, plant cell or plant. Inaddition, substrate may be sprayed on plant tissues expressing theappropriate enzymes. Using these various techniques, one may producePUFAs (e.g., n-6 unsaturated fatty acids such as AA, or n-3 fatty acidssuch as EPA or STA) by use of a plant cell, plant tissue or plant. Itshould also be noted that the invention also encompasses a transgenicplant comprising the above-described vector, wherein expression of thenucleotide sequence of the vector results in production of apolyunsaturated fatty acid in, for example, the seeds of the transgenicplant.

The substrates which may be produced by the host cell either naturallyor transgenically, as well as the enzymes which may be encoded by DNAsequences present in the vector which is subsequently introduced intothe host cell, are shown in FIG. 1.

In view of the above, the present invention encompasses a method ofproducing the desaturase enzymes (i.e., Δ5 or Δ6) comprising the stepsof: 1) isolating the nucleotide sequence of the gene encoding thedesaturase enzyme; 2) constructing a vector comprising said nucleotidesequence; and 3) introducing said vector into a host cell under time andconditions sufficient for the production of the desaturase enzyme.

The present invention also encompasses a method of producingpolyunsaturated fatty acids comprising exposing an acid to the enzymesuch that the desaturase converts the acid to a polyunsaturated fattyacid. For example, when 20:3n-6 is exposed to the Δ5-desaturase enzyme,it is converted to AA. AA may then be exposed to elongase whichelongates the AA to adrenic acid (i.e., 22:4n-6). Alternatively,Δ5-desaturase may be utilized to convert 20:4n-3 to 20:5n-3 which may beexposed to elongase and converted to (n-3)-docosapentaenoic acid. The(n-3)-docosapentaenoic acid may then be converted to DHA by use ofΔ4-desaturase. Thus, Δ5-desaturase may be used in the production ofpolyunsaturated fatty acids which may be used, in turn, for particularbeneficial purposes.

With respect to the role of Δ6-desaturase, linoleic acid may be exposedto the enzyme such that the enzyme converts the acid to GLA. An elongasemay then be used to convert the GLA to DGLA. The DGLA then may beconverted to AA by exposing the DGLA to a Δ5-desaturase. As anotherexample, ALA may be exposed to a Δ6-desaturase in order to convert theALA to STA. The STA may then be converted to 20:4n-3 by using anelongase. Subsequently, the 20:4n-3 may be converted to EPA by exposingthe 20:4n-3 to a Δ5-desaturase. Thus, the Δ6-desaturase may be used inthe production of PUFAs which have may advantageous properties or may beused in the production of other PUFAs.

Uses of the Δ5-Desaturases Genes, the Δ6-Desaturase Gene, and EnzymesEncoded Thereby

As noted above, the isolated desaturase genes and the desaturase enzymesencoded thereby have many uses. For example, the gene and correspondingenzyme may be used indirectly or directly in the production ofpolyunsaturated fatty acids, for example, Δ5-desaturase may be used inthe production of AA, adrenic acid or EPA. Delta-6 desaturase may beused either indirectly or directly in the production of GLA, DGLA, STAor 20:4n-3. (“Directly” is meant to encompass the situation where theenzyme directly converts the acid to another acid, the latter of whichis utilized in a composition (e.g., the conversion of DGLA to AA).“Indirectly” is meant to encompass the situation where an acid isconverted to another acid (i.e., a pathway intermediate) by thedesaturase (e.g., DGLA to AA) and then the latter acid is converted toanother acid by use of a non-desaturase enzyme (e.g., AA to adrenic acidby elongase or by use of another desaturase enzyme (e.g., AA to EPA byΔ17-desaturase.)). These polyunsaturated fatty acids (i.e., thoseproduced either directly or indirectly by activity of the desaturaseenzyme) may be added to, for example, nutritional compositions,pharmaceutical compositions, cosmetics, and animal feeds, all of whichare encompassed by the present invention. These uses are described, indetail, below.

Nutritional Compositions

The present invention includes nutritional compositions. Suchcompositions, for purposes of the present invention, include any food orpreparation for human consumption including for enteral or parenteralconsumption, which when taken into the body (a) serve to nourish orbuild up tissues or supply energy and/or (b) maintain, restore orsupport adequate nutritional status or metabolic function.

The nutritional composition of the present invention comprises at leastone oil or acid produced directly or indirectly by use of the desaturasegene, in accordance with the present invention, and may either be in asolid or liquid form. Additionally, the composition may include ediblemacronutrients, vitamins and minerals in amounts desired for aparticular use. The amount of such ingredients will vary depending onwhether the composition is intended for use with normal, healthyinfants, children or adults having specialized needs such as those whichaccompany certain metabolic conditions (e.g., metabolic disorders).

Examples of macronutrients which may be added to the composition includebut are not limited to edible fats, carbohydrates and proteins. Examplesof such edible fats include but are not limited to coconut oil, soy oil,and mono- and diglycerides. Examples of such carbohydrates include butare not limited to glucose, edible lactose and hydrolyzed search.Additionally, examples of proteins which may be utilized in thenutritional composition of the invention include but are not limited tosoy proteins, electrodialysed whey, electrodialysed skim milk, milkwhey, or the hydrolysates of these proteins.

With respect to vitamins and minerals, the following may be added to thenutritional compositions of the present invention: calcium, phosphorus,potassium, sodium, chloride, magnesium, manganese, iron, copper, zinc,selenium, iodine, and Vitamins A, E, D, C, and the B complex. Other suchvitamins and minerals may also be added.

The components utilized in the nutritional compositions of the presentinvention will be of semi-purified or purified origin. By semi-purifiedor purified is meant a material which has been prepared by purificationof a natural material or by synthesis.

Examples of nutritional compositions of the present invention includebut are not limited to infant formulas, dietary supplements, dietarysubstitutes, and rehydration compositions. Nutritional compositions ofparticular interest include but are not limited to those utilized forenteral and parenteral supplementation for infants, specialist infantformulas, supplements for the elderly, and supplements for those withgastrointestinal difficulties and/or malabsorption.

The nutritional composition of the present invention may also be addedto food even when supplementation of the diet is not required. Forexample, the composition may be added to food of any type including butnot limited to margarines, modified butters, cheeses, milk, yoghurt,chocolate, candy, snacks, salad oils, cooking oils, cooking fats, meats,fish and beverages.

In a preferred embodiment of the present invention, the nutritionalcomposition is an enteral nutritional product, more preferably, an adultor pediatric enteral nutritional product. This composition may beadministered to adults or children experiencing stress or havingspecialized needs due to chronic or acute disease states. Thecomposition may comprise, in addition to polyunsaturated fatty acidsproduced in accordance with the present invention, macronutrients,vitamins and minerals as described above. The macronutrients may bepresent in amounts equivalent to those present in human milk or on anenergy basis, i.e., on a per calorie basis.

Methods for formulating liquid or solid enteral and parenteralnutritional formulas are well known in the art. (See Also the ExamplesBelow.)

The enteral formula, for example, may be sterilized and subsequentlyutilized on a ready-to-feed (RTF) basis or stored in a concentratedliquid or powder. The powder can be prepared by spray drying the formulaprepared as indicated above, and reconstituting it by rehydrating theconcentrate. Adult and pediatric nutritional formulas are well known inthe art and are commercially available (e.g., Similac®, Ensure®, Jevity®and Alimentum® from Ross Products Division, Abbott Laboratories,Columbus, Ohio). An oil or acid produced in accordance with the presentinvention may be added to any of these formulas.

The energy density of the nutritional compositions of the presentinvention, when in liquid form, may range from about 0.6 Kcal to about 3Kcal per ml. When in solid or powdered form, the nutritional supplementsmay contain from about 1.2 to more than 9 Kcals per gram, preferablyabout 3 to 7 Kcals per gm. In general, the osmolality of a liquidproduct should be less than 700 mOsm and, more preferably, less than 660mOsm.

The nutritional formula may include macronutrients, vitamins, andminerals, as noted above, in addition to the PUFAs produced inaccordance with the present invention. The presence of these additionalcomponents helps the individual ingest the minimum daily requirements ofthese elements. In addition to the provision of PUFAs, it may also bedesirable to add zinc, copper, folic acid and antioxidants to thecomposition. It is believed that these substance boost a stressed immunesystem and will therefore provide further benefits to the individualreceiving the composition. A pharmaceutical composition may also besupplemented with these elements.

In a more preferred embodiment, the nutritional composition comprises,in addition to antioxidants and at least one PUFA, a source ofcarbohydrate wherein at least 5 weight percent of the carbohydrate isindigestible oligosaccharide. In a more preferred embodiment, thenutritional composition additionally comprises protein, taurine, andcarnitine.

As noted above, the PUFAs produced in accordance with the presentinvention, or derivatives thereof, may be added to a dietary substituteor supplement, particularly an infant formula, for patients undergoingintravenous feeding or for preventing or treating malnutrition or otherconditions or disease states. As background, it should be noted thathuman breast milk has a fatty acid profile comprising from about 0.15%to about 0.36% as DHA, from about 0.03% to about 0.13% as EPA, fromabout 0.30% to about 0.88% as AA, from about 0.22% to about 0.67% asDGLA, and from about 0.27% to about 1.04% as GLA. Thus, fatty acids suchas AA, EPA and/or docosahexaenoic acid (DHA), produced in accordancewith the present invention, can be used to alter, for example, thecomposition of infant formulas in order to better replicate the PUFAcontent of human breast milk or to alter the presence of PUFAs normallyfound in a non-human mammal's milk. In particular, a composition for usein a pharmacologic or food supplement, particularly a breast milksubstitute or supplement, will preferably comprise one or more of AA,DGLA and GLA. More preferably, the oil will comprise from about 0.3 to30% AA, from about 0.2 to 30% DGLA, and/or from about 0.2 to about 30%GLA.

Parenteral nutritional compositions comprising from about 2 to about 30weight percent fatty acids calculated as triglycerides are encompassedby the present invention. The preferred composition has about 1 to about25 weight percent of the total PUFA composition as GLA (U.S. Pat. No.5,196,198). Other vitamins, particularly fat-soluble vitamins such asvitamin A, D, E and L-carnitine can optionally be included. Whendesired, a preservative such as alpha-tocopherol may be added in anamount of about 0.1% by weight.

In addition, the ratios of AA, DGLA and GLA can be adapted for aparticular given end use. When formulated as a breast milk supplement orsubstitute, a composition which comprises one or more of AA, DGLA andGLA will be provided in a ratio of about 1:19:30 to about 6:1:0.2,respectively. For example, the breast milk of animals can vary in ratiosof AA:DGLA:GLA ranging from 1:19:30 to 6:1:0.2, which includesintermediate ratios which are preferably about 1:1:1, 1:2:1, 1:1:4. Whenproduced together in a host cell, adjusting the rate and percent ofconversion of a precursor substrate such as GLA and DGLA to AA can beused to precisely control the PUFA ratios. For example, a 5% to 10%conversion rate of DGLA to AA can be used to produce an AA to DGLA ratioof about 1:19, whereas a conversion rate of about 75% TO 80% can be usedto produce an AA to DGLA ratio of about 6:1. Therefore, whether in acell culture system or in a host animal, regulating the timing, extentand specificity of desaturase expression, as well as the expression ofother desaturases and elongases, can be used to modulate PUFA levels andratios. The PUFAs/acids produced in accordance with the presentinvention (e.g., AA and EPA) may then be combined with other PUFAs/acids(e.g., GLA) in the desired concentrations and ratios.

Additionally, PUFA produced in accordance with the present invention orhost cells containing them may also be used as animal food supplementsto alter an animal's tissue or milk fatty acid composition to one moredesirable for human or animal consumption.

Pharmaceutical Compositions

The present invention also encompasses a pharmaceutical compositioncomprising one or more of the acids and/or resulting oils produced usingthe desaturase genes, in accordance with the methods described herein.More specifically, such a pharmaceutical composition may comprise one ormore of the acids and/or oils as well as a standard, well-known,non-toxic pharmaceutically acceptable carrier, adjuvant or vehicle suchas, for example, phosphate buffered saline, water, ethanol, polyols,vegetable oils, a wetting agent or an emulsion such as a water/oilemulsion. The composition may be in either a liquid or solid form. Forexample, the composition may be in the form of a tablet, capsule,ingestible liquid or powder, injectible, or topical ointment or cream.Proper fluidity can be maintained, for example, by the maintenance ofthe required particle size in the case of dispersions and by the use ofsurfactants. It may also be desirable to include isotonic agents, forexample, sugars, sodium chloride and the like. Besides such inertdiluents, the composition can also include adjuvants, such as wettingagents, emulsifying and suspending agents, sweetening agents, flavoringagents and perfuming agents.

Suspensions, in addition to the active compounds, may comprisesuspending agents such as, for example, ethoxylated isostearyl alcohols,polyoxyethylene sorbitol and sorbitan esters, microcrystallinecellulose, aluminum metahydroxide, bentonite, agar-agar and tragacanthor mixtures of these substances.

Solid dosage forms such as tablets and capsules can be prepared usingtechniques well known in the art. For example, PUFAs produced inaccordance with the present invention can be tableted with conventionaltablet bases such as lactose, sucrose, and cornstarch in combinationwith binders such as acacia, cornstarch or gelatin, disintegratingagents such as potato starch or alginic acid, and a lubricant such asstearic acid or magnesium stearate. Capsules can be prepared byincorporating these excipients into a gelatin capsule along withantioxidants and the relevant PUFA(s). The antioxidant and PUFAcomponents should fit within the guidelines presented above.

For intravenous administration, the PUFAs produced in accordance withthe present invention or derivatives thereof may be incorporated intocommercial formulations such as Intralipids™. The typical normal adultplasma fatty acid profile comprises 6.64 to 9.46% of AA, 1.45 to 3.11%of DGLA, and 0.02 to 0.08% of GLA. These PUFAs or their metabolicprecursors can be administered alone or in combination with other PUFAsin order to achieve a normal fatty acid profile in a patient. Wheredesired, the individual components of the formulations may be providedindividually, in kit form, for single or multiple use. A typical dosageof a particular fatty acid is from 0.1 mg to 20 g (up to 100 g) dailyand is preferably from 10 mg to 1, 2, 5 or 10 g daily.

Possible routes of administration of the pharmaceutical compositions ofthe present invention include, for example, enteral (e.g., oral andrectal) and parenteral. For example, a liquid preparation may beadministered, for example, orally or rectally. Additionally, ahomogenous mixture can be completely dispersed in water, admixed understerile conditions with physiologically acceptable diluents,preservatives, buffers or propellants in order to form a spray orinhalant. The route of administration will, of course, depend upon thedesired effect. For example, if the composition is being utilized totreat rough, dry, or aging skin, to treat injured or burned skin, or totreat skin or hair affected by a disease or condition, it may perhaps beapplied topically.

The dosage of the composition to be administered to the patient may bedetermined by one of ordinary skill in the art and depends upon variousfactors such as weight of the patient, age of the patient, immune statusof the patient, etc.

With respect to form, the composition may be, for example, a solution, adispersion, a suspension, an emulsion or a sterile powder which is thenreconstituted.

The present invention also includes the treatment of various disordersby use of the pharmaceutical and/or nutritional compositions describedherein. In particular, the compositions of the present invention may beused to treat restenosis after angioplasty. Furthermore, symptoms ofinflammation, rheumatoid arthritis, asthma and psoriasis may also betreated with the compositions of the invention. Evidence also indicatesthat PUFAs may be involved in calcium metabolism; thus, the compositionsof the present invention may, perhaps, be utilized in the treatment orprevention of osteoporosis and of kidney or urinary tract stones.

Additionally, the compositions of the present invention may also be usedin the treatment of cancer. Malignant cells have been shown to havealtered fatty acid compositions. Addition of fatty acids has been shownto slow their growth, cause cell death and increase their susceptibilityto chemotherapeutic agents. Moreover, the compositions of the presentinvention may also be useful for treating cachexia associated withcancer.

The compositions of the present invention may also be used to treatdiabetes (see U.S. Pat. No. 4,826,877 and Horrobin et al., Am. J. Clin.Nutr. Vol. 57 (Suppl.) 732S-737S). Altered fatty acid metabolism andcomposition have been demonstrated in diabetic animals.

Furthermore, the compositions of the present invention, comprising PUFAsproduced either directly or indirectly through the use of the desaturaseenzymes, may also be used in the treatment of eczema, in the reductionof blood pressure, and in the improvement of mathematics examinationscores. Additionally, the compositions of the present invention may beused in inhibition of platelet aggregation, induction of vasodilation,reduction in cholesterol levels, inhibition of proliferation of vesselwall smooth muscle and fibrous tissue (Brenner et al., Adv. Exp. Med.Biol. Vol. 83, p. 85-101, 1976), reduction or prevention ofgastrointestinal bleeding and other side effects of non-steroidalanti-inflammatory drugs (see U.S. Pat. No. 4,666,701), prevention ortreatment of endometriosis and premenstrual syndrome (see U.S. Pat. No.4,758,592), and treatment of myalgic encephalomyelitis and chronicfatigue after viral infections (see U.S. Pat. No. 5,116,871).

Further uses of the compositions of the present invention include use inthe treatment of AIDS, multiple sclerosis, and inflammatory skindisorders, as well as for maintenance of general health.

Additionally, the composition of the present invention may be utilizedfor cosmetic purposes. It may be added to pre-existing cosmeticcompositions such that a mixture is formed or may be used as a solecomposition.

Veterinary Applications

It should be noted that the above-described pharmaceutical andnutritional compositions may be utilized in connection with animals(i.e., domestic or non-domestic), as well as humans, as animalsexperience many of the same needs and conditions as humans. For example,the oil or acids of the present invention may be utilized in animal feedsupplements, animal feed substitutes, animal vitamins or in animaltopical ointments.

The present invention may be illustrated by the use of the followingnon-limiting examples:

Example 1 Design of Degenerate Oligonucleotides for the Isolation ofDesaturases from Fungi and cDNA Library Construction

Analysis of the fatty acid composition of Saprolegnia diclina (S.diclina)(ATCC 56851) revealed the presence of a considerable amount ofarachidonic acid (ARA, 20:4 n-6) and eicosapentanoic acid (EPA, 20:5n-3). Thus, it was thought that this organism contained an activeΔ6-desaturase capable of converting linoleic acid (LA, 18:2 n-6) togamma-linolenic acid (GLA, 18:3 n-6), and an active Δ5-desaturase thatwould convert dihomo-gamma-linolenic acid (DGLA, 20:3 n-6) toarachidonic acid (ARA, 20:4 n-6) (FIG. 1). In addition, it was thoughtthat S. diclina also contained a Δ17-desaturase capable of desaturatingARA to EPA.

The fatty acid composition analysis of Thraustochytrium aureum (T.aureum) (ATCC 34304) revealed not only ARA and EPA but also longer chainPUFAs such as adrenic acid (ADA, 22:4n-6), ω6-docosapentaenoic acid(ω6-DPA, 22:5n-6), (ω3-docosapentaenoic acid (ω3-DPA, 22:5n-3), anddocosahexaenoic acid (DHA, 22:6n-3). Thus, in addition to Δ6-, Δ5- andΔ17-desaturases, it was thought that T. aureum perhaps contained aΔ19-desaturase which converts ADA to ω3-DPA or ω6-DPA to DHA and/or aΔ4-desaturase which desaturates ADA to ω6-DPA or ω3-DPA to DHA. The goalthus was to attempt to isolate these predicted desaturase genes from S.diclina and T. aureum, and eventually to verify the functionality byexpression in an alternate host.

To isolate genes encoding functional desaturase enzymes, a cDNA librarywas constructed for each organism. Saprolegnia diclina (ATCC 56851)cultures were grown in potato dextrose media Difco #336 (DifcoLaboratories, Detroit, Mich.) at room temperature for 4 days withconstant agitation. The mycelia were harvested by filtration throughseveral layers of cheese cloth, and the cultures crushed in liquidnitrogen using a mortar and pestle. Total RNA was purified from it usingthe Qiagen RNeasy Maxi kit (Qiagen, Valencia, Calif.) as permanufacturer's protocol.

T. aureum (ATCC 34304) cells were grown in BY+ Media (Difco #790) atroom temperature for 4 days, in the presence of light, and with constantagitation (250 rpm) to obtain the maximum biomass. These cells wereharvested by centrifugation at 5000 rpm for 10 minutes and rinsed inice-cold RNase-free water. These cells were then lysed in a French pressat 10,000 psi, and the lysed cells directly collected into TE bufferedphenol. Proteins from the cell lysate were removed by repeatedphenol:chloroform (1:1 v/v) extraction, followed by a chloroformextraction. The nucleic acids from the aqueous phase were precipitatedout at −70° C. for 30 minutes using 0.3M (final concentration) sodiumacetate (pH 5.6) and one volume of isopropanol. The precipitated nucleicacids were collected by centrifugation at 15,000 rpm for 30 minutes at4° C., vacuum-dried for 5 minutes and then treated with DNaseI(RNase-free) in 1×DNase buffer (20 mM Tris-Cl, pH 8.0; 5 mM MgCl₂) for15 minutes at room temperature. The reaction was quenched with 5 mM EDTA(pH 8.0) and the RNA further purified using the Qiagen RNeasy Maxi kit(Qiagen, Valencia, Calif.) as per the manufacturer's protocol.

mRNA was isolated from total RNA from each organism using oligo dTcellulose resin. The pBluescript II XR library construction kit(Stratagene, La Jolla, Calif.) was then used to synthesize doublestranded cDNA which was then directionally cloned (5′ EcoRI/3′ XhoI)into pBluescript II SK(+) vector. The S. diclina and T. aureum librariescontained approximately 2.5×10⁶ clones each with an average insert sizeof approximately 700 bp. Genomic DNA from PUFA producing cultures of S.diclina and T. aureum was isolated by crushing the culture in liquidnitrogen and purified using Qiagen Genomic DNA Extraction Kit (Qiagen,Valencia, Calif.).

The approach taken was to design degenerate oligonucleotides (i.e.,primers) that represent amino acid motifs that are conserved in knowndesaturases. These primers could be used in a PCR reaction to identify afragment containing the conserved regions in the predicted desaturasegenes from fungi. Since the only fungal desaturases identified are Δ5-and Δ6-desaturase genes from Mortierella alpina (Genbank accessionnumbers AF067650, AB020032, respectively), desaturase sequences fromplants as well as animals were taken into consideration during thedesign of these degenerate primers. Known Δ5- and Δ6-desaturasesequences from the following organisms were used for the design of thesedegenerate primers: Mortierella alpina, Borago officinalis, Helianthusannuus, Brassica napus, Dictyostelium discoideum, Rattus norvegicus, Musmusculus, Homo sapien, Caenorhabditis elegans, Arabidopsis thaliana, andRicinus communis. The degenerate primers used were as follows using theCODEHOP Blockmaker program (http://blocks.fhcrc.org/codehop.html):

A. Protein motif 1: NH₃-VYDVTEWVKRHPGG-COOHPrimer RO 834 (SEQ ID NO: 1):5′-GTBTAYGAYGTBACCGARTGGGTBAAGCGYCAYCCBGGHGGH-3′B. Protein Motif 2: NH₃-GASANWWKHQHNVHH-COOHPrimer RO835 (Forward) (SEQ ID NO: 2):5′-GGHGCYTCCGCYAACTGGTGGAAGCAYCAGCAYAACGTBCAYCAY- 3′Primer RO836 (Reverse) (SEQ ID NO: 3)5′-RTGRTGVACGTTRTGCTGRTGCTTCCACCAGTTRGCGGARGCDCC- 3′C. Protein Motif 3: NH₃-NYQIEHHLFPTM-COOHPrimer RO838 (Reverse) (SEQ ID NO: 4)5T-TTGATRGTCTARCTYGTRGTRGASAARGGVTGGTAC-3′

-   -   In addition, two more primers were designed based on the 2nd and        3rd conserved ‘Histidine-box’ found in known Δ6-desaturases.        These were:

Primer RO753 5′-CATCATCATXGGRAAXARRTGRTG-3′ (SEQ ID NO: 5) Primer RO7545′-CTACTACTACTACAYCAYACXTAYACXAAY-3′ (SEQ ID NO: 6)

-   -   The degeneracy code for the oligonucleotide sequences was: B=C,        G, T; H=A, C, T; S═C,G; R=A,G; V=A, C, G; Y═C,T; D=A+T+C; X=A,        C, G, T

Example 2 Isolation of Δ6-Desaturase Nucleotide Sequences fromSaprolegnia diclina (ATCC 56851)

Total RNA from Saprolegnia diclina (ATCC 56851) was isolated using thelithium chloride method (Hoge, et al., Exp. Mycology (1982) 6:225-232).Five μg of the total RNA was reverse transcribed, using the SuperScriptPreamplification system (LifeTechnologies, Rockville, Md.) and theoligo(dT)₁₂₋₁₈ primer supplied with the kit, to generate the firststrand cDNA.

To isolate the Δ6-desaturase gene, various permutations and combinationsof the above mentioned degenerate oligonucleotides were used in PCRreactions. Of the various primer sets tried, the only primers to givedistinct bands were RO834/RO838. PCR amplification was carried out in a100 μl volume containing: 2 μl of the first strand cDNA template, 20 mMTris-HCl, pH 8.4, 50 mM KCl, 1.5 mM MgCl₂, 200 μm eachdeoxyribonucleotide triphosphate and 2 pmole of each primer.Thermocycling was carried out at two different annealing temperatures,42° C. and 45° C., and these two PCR reactions were combined, resolvedon a 1.0% agarose gel, and the band of −1000 bp was gel purified usingthe QiaQuick Gel Extraction Kit (Qiagen, Valencia, Calif.). Thestaggered ends on these fragments were ‘filled-in’ using T4 DNApolymerase (LifeTechnologies, Rockville, Md.) as per manufacturer'sspecifications, and these DNA fragments were cloned into the PCR-Bluntvector (Invitrogen, Carlsbad, Calif.). The recombinant plasmids weretransformed into TOP10 supercompetent cells (Invitrogen, Carlsbad,Calif.), and clones were sequenced.

Two clones were thus isolated that showed sequence homology topreviously identified Δ6-desaturases. These clones are described asfollows:

-   -   a. Clone#20-2 was partially sequenced and the deduced amino acid        sequence from 702 by showed 30.2% identity with Δ6-desaturase        from Mortierella alpina as the highest scoring match in a TfastA        search.    -   b. Clone #30-1 was partially sequenced, and the deduced amino        acid sequence of 687 by showed 48.5% amino acid identity with        Mortierella alpina's Δ6-desaturase as the highest scoring match        in a TfastA search. These two sequences also overlapped each        other indicating they belonged to a single putative        Δ6-desaturase from S. diclina. This novel Δ6-desaturase sequence        was then used to design primers to retrieve the 3′- and the        5′-end of the full-length Δ6-desaturase gene from the cDNA        library generated from the mRNA of S. diclina.

To isolate the 3′-end, PCR amplification was carried out using plasmidDNA purified from the cDNA library as the template and oligonucleotidesRO0923 (SEQ ID NO:7) (5′-CGGTGCAGTGGTGGAAGAACAAGCACAAC-3′) and RO899(SEQ ID NO:8) (5′-AGCGGATAACAATTTCACACAGGAAACAGC-3′). OligonucleotideRO923 was designed based on the #20-2 fragment of this putativeΔ6-desaturase, and oligonucleotide RO899 corresponded to sequence fromthe pBluescript II SK(+) vector used for preparation of the cDNAlibrary. Amplification was carried out using 10 pmols of each primer andthe Taq PCR Master Mix (Qiagen, Valencia, Calif.). Samples weredenatured initially at 94° C. for 3 minutes, followed by 30 cycles ofthe following: 94° C. for 1 minute, 60° C. for 1 minute, 72° C. for 2minutes. A final extension cycle at 72° C. for 10 minutes was carriedout before the reaction was terminated. The PCR fragments were resolvedon a 0.8% agarose gel and gel purified using the Qiagen Gel ExtractionKit. The staggered end on these fragments were ‘filled-in’ using T4 DNApolymerase (LifeTechnologies, Rockville, Md.) as per manufacturer'sspecifications, and these DNA fragments were cloned into the PCR-Bluntvector (Invitrogen, Carlsbad, Calif.). The recombinant plasmids weretransformed into TOP10 supercompetent cells (Invitrogen, Carlsbad,Calif.), and clones were sequenced. Clone sd2-2 contained a 958 byinsert which was identified to contain the 3′-end of the putativeΔ6-gene based on sequence homology with known Δ6-desaturases and thepresence of the ‘TAA’ stop codon and Poly A tail.

To isolate the 5′-end of this Δ6-desaturase from Saprolegnia diclina,the oligonucleotide RO939 (SEQ ID NO:9)(5′-CGTAGTACTGCTCGAGGAGCTTGAGCGCCG-3′) was designed based on thesequence of the #30-1 fragment identified earlier. This oligonucleotidewas used in combination with RO898 (SEQ ID NO:10)(5′-CCCAGTCACGACGTTGTAAAACGACGGCCAG-3′) (designed based on the sequenceof from the pBluescript SK(+) vector) to PCR amplify the 5′-end of theΔ6-desaturase from the cDNA library. In this case, the Advantage-GC cDNAPCR kit (Clonetech, Palo Alto, Calif.) was used to overcome PCRamplification problems that occur with GC rich regions, predicted to bepresent at the 5′-end of this β6-desaturase. PCR thermocyclingconditions were as follows: The template was initially denatured at 94°C. for 1 minute, followed by 30 cycles of [94° C. for 30 seconds, 68° C.for 3 minutes], and finally an extension cycle at 68° C. for 5 minutes.The PCR products thus obtained were cloned into the PCR-Blunt vector(Invitrogen, Carlsbad, Calif.) following the same protocol as describedabove. Clone sd21-2 was thus obtained that contained a 360 by insertthat contained the putative ‘ATG’ start site of the novel Δ6-desaturase.The deduced amino acid sequence of this fragment, when aligned withknown Δ6-desaturases showed 37-45% identity.

This novel Δ6-desaturase gene was isolated in its entirety by PCRamplification using, the S. diclina cDNA library, or S. diclina genomicDNA as a template, and the following oligonucleotides:

a. RO 951 (5′-TCAACAGAATTCATGGTCCAGGGGCAAAAGGCCGAGAAGATCTCG-3′)(SEQ ID NO: 11)

-   -   that contained sequence from the 5′ end of clone sd21-2 as well        as an EcoRI site (underlined) to facilitate cloning into a yeast        expression vector

b. RO960 (5′-ATACGTAAGCTTTTACATGGCGGGAAACTCCTTGAAGAACTCGATCG-3′)(SEQ ID NO: 12)

-   -   that contained sequence from the 3′ end of clone sd2-2 including        the stop codon as well as a Hindi=site (underlined) for cloning        in an expression vector.        PCR amplification was carried out using 200 ng of the cDNA        library plasmid template, 10 pmoles of each primer and the Taq        PCR Master Mix (Qiagen, Valencia, Calif.), or 200 ng of genomic        DNA, 10 pmoles of each primer, and the Advantage-GC cDNA PCR kit        (Clonetech, Palo Alto, Calif.). Thermocycling conditions were as        follows: the template was initially denatured at 94° C. for 1        minute, followed by 30 cycles of [94° C. for 30 seconds, 68° C.        for 3 minutes], and finally an extension cycle at 68° C. for 5        minutes. The PCR product thus obtained was digested with        EcoRI/HindIII and cloned into the yeast expression vector pYX242        (Invitrogen, Carlsbad, Calif.) to generate clones pRSP1 (genomic        DNA-derived) and pRSP2 (library-derived) which were then        sequenced and used for expression studies.

The Δ6-desaturase full-length gene insert was 1362 by (SEQ ID NO:13,FIG. 2) in length and, beginning with the first ATG, contained an openreading frame encoding 453 amino acids. (The nucleotide sequenceencoding the Δ6-desaturase was deposited with the American Type CultureCollection (ATCC), 10801 University Boulevard, Manassas, Va. 20110 underthe terms of the Budapest Treaty on Jan. 23, 2001 and was accordedaccession number PTA-2929.) The amino acid sequence of the full-lengthgene (SEQ ID NO:14, FIG. 3) contained regions of homology toΔ6-desaturases from Mortierella alpina, Caenorhabditis elegans andBorago officinalis. It also contained the three conserved ‘histidineboxes’ found in all known membrane-bound desaturases (Okuley, et al.(1994) The Plant Cell 6: 147-158). These were present at amino acidpositions 171-176, 208-212, and 391-395. As with other membrane-boundΔ6-desaturases, the third Histidine-box motif (HXXHH) in the S. diclinaΔ6-desaturase was found to be QXXHH. This sequence also contained acytochrome b5 domain at the 5′-end. This cytochrome b5 domain is foundin a number of membrane-bound desaturase enzymes, and cytochrome b5 isthought to function as an electron donor in these enzymes. The presenceof this domain may be advantageous when expressing the desaturase inheterologous systems for PUFA production. Since the proposed use of thisgene is for the reconstruction of the PUFA biosynthetic pathway inplants, the base composition of this gene may be important. (It is knownthat some recombinant genes show poor expression because of variationsin their base composition as compared to that of the host. The overallG+C content of this gene was 59%, which is close to that of the M.alpina desaturases that have been successfully expressed in plants.)

Example 3 Isolation of Δ5-Desaturase Nucleotide Sequences fromSaprolegnia diclina (ATCC 56851)

Saprolegnia diclina (ATCC 56851) produces both arachidonic acid (ARA,20:4 n-6) and eicosapentanoic acid (EPA, 20:5 n-3); thus, it was thoughtto have, perhaps, a Δ5-desaturase which can convertdihomo-gamma-linolenic acid (DGLA, 20:3n-6) to arachidonic acid (ARA,20:4 n-6). As with the Δ6-desaturase isolation, for the β5-desaturaseisolation from S. diclina, various combinations of the degenerateprimers were used in PCR reactions, using first strand cDNA as thetemplate. The primer combination, RO753 and RO754, generated a distinctband of 588 by using the following PCR conditions: 2 μl of the firststrand cDNA template, 20 mM Tris-HCl, pH 8.4, 50 mM KCl, 1.5 mM MgCl₂,200 μM each deoxyribonucleotide triphosphate, 2 pmole of each primer and1U cDNA polymerase (Clonetech, Palo Alto, Calif.), in a final reactionvolume of 50 μl. Thermocycling was carried out as follows: an initialdenaturation at 94° C. for 3 minutes, followed by 35 cycles of:denaturation at 94° C. for 30 seconds, annealing at 60° C. for 30seconds and extension at 72° C. for 1 minute. This was followed by afinal extension at 72° C. for 7 minutes, and the reaction was terminatedat 4° C. This fragment thus generated was cloned (clone #18-1),sequenced and, when translated, showed 43% amino acid identity withMortierella alpina Δ5-desaturase (Genbank accession # AF067654) and38.7% identity with Dictyostelium discoideum Δ5-desaturase (Genbankaccession # AB029311). The second PCR fragment was identified usingPrimers RO834 and RO838 in the reaction described in Example 2. Thisfragment, of approximately 1000 by in length, was cloned (Clone #20-8)and the deduced amino acid sequence derived from 775 by showed 42%identity with Δ5-desaturase from Dictyostelium discoideum Δ5-desaturase(Genbank accession # AB029311). These two sequences, #18-1 and #20-8,overlapped each other indicating they belonged to a single putativeΔ5-desaturase from S. diclina. These sequences were then used to designprimers to retrieve the 3′- and the 5′-end of the novel Δ5-desaturasegene from the cDNA library generated from the mRNA of S. diclina.

To isolate the 3′-end of this putative Δ5-desaturase, PCR amplificationwas carried out using plasmid DNA purified from the cDNA library, as thetemplate and oligonucleotides RO851 (SEQ ID NO:15)(5′-CCATCAAGACGTACCTTGCGATC-3′) and RO899 (SEQ ID NO:8)(5′-AGCGGATAACAATTTCACACAGGAAACAGC-3′). Oligonucleotide RO851 wasdesigned based on the #18-1 fragment of this putative Δ5-desaturase, andoligonucleotide RO899 corresponded to sequence from the pBluescript IISK(+) vector. Amplification was carried out using 200 ng of templateplasmid DNA, 10 pmoles of each primer and the Tag PCR Master Mix(Qiagen, Valencia, Calif.). Samples were denatured initially at 94° C.for 3 minutes, followed by 35 cycles of the following: 94° C. for 30seconds, 60° C. for 30 seconds, 72° C. for 1 minutes. A final extensioncycle at 72° C. for 7 minutes was carried out before the reaction wasterminated. The PCR fragments were cloned into the PCR-Blunt vector(Invitrogen, Carlsbad, Calif.) as per the protocol described in Example2. The recombinant plasmids were transformed into TOP10 supercompetentcells (Invitrogen, Carlsbad, Calif.), and clones were sequenced. Clonesd12-11 contained a 648 by insert which contained the 3′-end of theputative Δ5-gene based on sequence homology with known Δ5-desaturasesand the presence of the ‘TAA’ stop codon and polyA tail.

The 5′-end of this Δ5-desaturase from Saprolegnia diclina was isolatedusing primers RO941 and RO898. The oligonucleotide RO941 (SEQ ID NO:16)(5′-GCTGAACGGGTGGTACGAGTCGAACGTG-3′) was designed based on the sequenceof the #20-8 fragment identified earlier. This oligonucleotide was usedin combination with RO898 (SEQ ID NO:10)(5′-CCCAGTCACGACGTTGTAAAACGACGGCCAG-3′) (designed based on the sequenceof from the pBluescript II SK(+) vector) in a PCR amplification reactionusing the cDNA library plasmid DNA as the template. Here theAdvantage-GC cDNA PCR kit (Clonetech, Palo Alto, Calif.) was used as perthe manufacturer's protocol, and the thermocycling conditions were asfollows: an initial denaturation was carried out at 94° C. for 1 minute,followed by 30 cycles of [denaturation at 94° C. for 30 seconds,annealing and extension 68° C. for 3 minutes], and a final extensioncycle at 68° C. for 5 minutes. These PCR products were purified, clonedinto the PCR-Blunt vector (Invitrogen, Carlsbad, Calif.), and sequencedas described above. Clone sd24-1 was identified to contain a 295 byinsert that contained the putative ‘ATG’ start site of the novelΔ5-desaturase. Analysis of the deduced amino acid sequence of thisfragment showed regions of high homology with known Δ5-desaturases andalso the presence of a cytochrome b5 domain.

The full-length Δ5-desaturase gene was isolated by PCR amplificationusing S. diclina genomic DNA as a template and the followingoligonucleotides:

a. RO953 (SEQ ID NO: 17)(5′-ACGAGAGAATTCATGGCCCCGCAGACGGAGCTCCGCCAGCGC-3′)

-   -   that contained sequence from the 5′ end of clone sd24-1 as well        as an EcoRI site (underlined) to facilitate cloning into a yeast        expression vector; and

b. RO956 (5′-AAAAGACTCGAGTTAGCCCATGTGGATCGTGGCGGCGATGCCCTGC-3′)(SEQ ID NO: 18)

-   -   that contained sequence from the 3′ end of clone sd12-11        including the stop codon as well as a XhoI site (underlined) for        cloning in an expression vector.        Conditions for the PCR amplification of the ‘full length’ gene        were similar to those described for the amplification of the        Δ6-desaturase from genomic DNA (Example 2). The PCR product thus        obtained was digested with EcoRI/XhoI and cloned into the yeast        expression vector pYX242 (Invitrogen, Carlsbad, Calif.). Clone        pRSP3 (genomic DNA-derived) was shown to contain a 1413 by        insert and was used for expression studies.

The 1413 by full-length gene (SEQ ID NO:19, FIG. 4) of the putativeΔ5-desaturase from S. diclina contained an open reading frame encoding471 amino acids (SEQ ID NO:20, FIG. 5). (The nucleotide sequenceencoding the Δ5-desaturase was deposited with the ATCC, 10810 UniversityBoulevard, Manassas, Va. 20110 under the terms of the Budapest Treaty onJan. 23, 2001 and was accorded accession number PTA-2928.) Thistranslated protein showed 40.5% overall identity with the Mortierellaalpina Δ5-desaturasae (Genbank accession # AF067654) and 39.5% identitywith the Dictyostelium discoideum Δ5-desaturase (Genbank accession #AB022097). It also contained the three conserved ‘histidine boxes’ atamino acid positions 186-190, 223-228, 406-410. Like the Δ6-desaturase,this sequence also contained a cytochrome b5 domain at the 5′-end. Theoverall G+C content of this gene was 61.5%.

Example 4 Expression of S. diclina Desaturase Genes in Baker's Yeast

Clone pRSP2, which consisted of the full length Δ6-desaturase clonedinto PYX242 (Invitrogen, Carlsbad, Calif.), and clone pRSP3, whichconsisted of the full-length Delta 5-desaturase gene in pYX242, weretransformed into competent Saccharomyces cerevisiae strain 334. Yeasttransformation was carried out using the Alkali-Cation YeastTransformation Kit (BIO 101, Vista, Calif.) according to conditionsspecified by the manufacturer. Transformants were selected for leucineauxotrophy on media lacking leucine (DOB [-Leu]). To detect the specificdesaturase activity of these clones, transformants were grown in thepresence of 50 μM specific fatty acid substrates as listed below:

-   -   a. Stearic acid (18:0) (conversion to oleic acid would indicate        Δ9-desaturase activity)    -   b. Oleic acid (18:1) (conversion to linoleic acid would        indicated Δ12-desaturase activity)    -   c. Linoleic acid (18:2 n-6) (conversion to alpha-linolenic acid        would indicate Δ15-desaturase activity and conversion to        gamma-linolenic acid would indicate Δ6-desaturase activity)    -   d. Alpha-linolenic acid (18:3 n-3) (conversion to stearidonic        acid would indicate Δ6-desaturase activity)    -   e. Dihomo-gamma-linolenic acid (20:3 n-6) (conversion to        arachidonic acid would indicate Δ5-desaturase activity).        The negative control strain was S. cerevisiae 334 containing the        unaltered pYX242 vector, and these were grown simultaneously.        The cultures were vigorously agitated (250 rpm) and grown for 48        hours at 24° C. in the presence of 50 μm (final concentration)        of the various substrates. The cells were pelleted and vortexed        in methanol; chloroform was added along with tritridecanoin (as        an internal standard). These mixtures were incubated for at        least an hour at room temperature or at 4° C. overnight. The        chloroform layer was extracted and filtered through a Whatman        filter with 1 μM anhydrous sodium sulfate to remove particulates        and residual water. The organic solvents were evaporated at        40° C. under a stream of nitrogen. The extracted lipids were        then derivatized to fatty acid methyl esters (FAME) for gas        chromatography analysis (GC) by adding 2 ml of 0.5 N potassium        hydroxide in methanol to a closed tube. The samples were heated        to 95° C.-100° C. for 30 minutes and cooled to room temperature.        Approximately 2 ml of 14% borontrifluoride in methanol were        added and the heating repeated. After the extracted lipid        mixture cooled, 2 ml of water and 1 ml of hexane were added to        extract the FAME for analysis by GC. The percent conversion was        calculated by dividing the product produced by the sum of (the        product produced+the substrate added) and then multiplying by        100.

Table 1 represents the enzyme activity of the genes isolated based onthe percent conversion of substrate added. The pRSP1 clone thatcontained the Δ6-desaturase gene from S. diclina converted 28% of the18:2n-6 substrate to 18:3n-3, as well was 37% of the 18:3n-3 substrateto 18:4n-3. This confirms that the gene encodes a Δ6-desaturase. Therewas no background (non-specific conversion of substrate) in this case.(All tables referred to herein are presented after the Abstract of theDisclosure.)

The pRSP3 clone that contained the Δ5-desaturase gene from S. diclinawas capable of converting 27% of the added 20:3n-6 substrate to 20:4n-6,indicating that the enzyme it encodes is a Δ5-desaturase. In this casetoo, there was no background substrate conversion detected. This dataindicates that desaturases with different substrate specificity can beexpressed in a heterologous system and can also be used to producepolyunsaturated fatty acids.

Table 2 represents fatty acids of interest as a percentage of the totallipid extracted from S. cerevisiae 334 with the indicated plasmid. Noglucose was present in the growth media. Affinity gas chromatography wasused to separate the respective lipids. GC/MS was employed to identifythe products. From this table, it is apparent that exogenously addedsubstrates, when added in the free form was taken up by the recombinantyeast and the incorporated into their membranes. In the yeast clonecontaining the Δ6-desaturase gene (pRSP1), GLA (γ-18:3) was identifiedas a novel PUFA when LA (18:2) was added as the substrate, andarachidonic acid was detected in yeast containing the Δ5-desaturase gene(pRSP3) when DGLA (20:3) was added as a substrate.

Example 5 Co-Expression of S. diclina Desaturases with Elongases

The plasmid pRSP1 (Δ6) and pRSP3 (Δ5) were individually co-transformedwith pRAE73-Δ3, a clone that contains the Human Elongase gene (SEQ IDNO:21) in the yeast expression vector pYES2, into yeast as described inExample 4. This elongase gene catalyzes some of the elongation steps inthe PUFA pathway. Co-transformants were selected on minimal medialacking leucine and uracil (DOB[-Leu-Ura]).

Table 3 shows that when 50 μM of the substrate LA (18:2 n-6) was added,that the Δ6-desaturase converted this substrate to GLA (18:3 n-6) andthe elongase was able to add two carbons to GLA to produce DGLA (20:3n-6). The percent conversion of the substrate to the final product bythese co-transformed enzymes is 26.4%, with no background observed fromthe negative control. Similarly, the co-transformed enzymes can act onALA (18:3n-3) to finally form (20:4n-3) with a percentage conversion of34.39%. Thus, S. diclina Δ6-desaturase was able to produce a product ina heterologous expression system that could be further utilized byanother heterologous enzyme from the PUFA biosynthetic pathway toproduce the expected PUFA.

Table 4 shows results of the pRSP3(Δ5)/Human Elongase co-transformationexperiment. In this case, substrate GLA (18:3n-6) was converted to DGLA(20:3n-6) by human elongase and this was further converted to ARA(20:4n-6) by the action of S. diclina Δ5-desaturase. The percentconversion of the substrate to the final product by these co-transformedenzymes is 38.6%, with no background observed from the negative control.

The other substrate tested in this case was STA (18:4 n-3) which waseventually converted to EPA (20:5n-3) by the concerted action of the twoenzymes. Similar results were observed when the pRSP1 and pRSP3 werecotransformed with an elongase gene derived from M. alpina (pRPB2) (SEQID NO:22), and both genes were shown to be functional in the presence ofeach other (see Table 3 and Table 4).

Example 6 Isolation of Δ5-Desaturase Nucleotide Sequences fromThraustochytrium aureum (ATCC 34303)

To isolate putative desaturase genes, total RNA was Isolated asdescribed in Example 2. Approximately 5 μg was reverse transcribed usingthe SuperScript Preamplification system (LifeTechnologies, Rockville,Md.) as shown in Example 2 to produce first strand cDNA. Using thedegenerate primers RO834 (SEQ ID NO:1) and 838 (SEQ ID NO:4) designedwith the block maker program in a 50 μl reaction, the followingcomponents were combined: 2 μl of the first strand cDNA template, 20 mMTris-HCl, pH 8.4, 50 mM KCl, 1.5 mM MgCl₂, 200 μM eachdeoxyribonucleotide triphosphate, 2 pmole final concentration of eachprimer and cDNA polymerase (Clonetech, Palo Alto, Calif.). Thermocyclingwas carried out as follows: an initial denaturation at 94° C. for 3minutes, followed by 35 cycles of denaturation at 94° C. for 30 seconds,annealing at 60° C. for 30 seconds and extension at 72° C. for 1 minute.This was followed by a final extension at 72° C. for 7 minutes. Twofaint bands of approximately 1000 by were separated on a 1% agarose gel,excised, and purified with the QiaQuick Gel Extraction Kit (Qiagen,Valencia, Calif.). The ends were filled in with T4 DNA polymerase andthe blunt-end fragments cloned into PCR Blunt as described in Example 2.Sequencing of the obtained clones identified the partial sequence of 680by from clone 30-9 whose translation of 226 amino acids had 31.5%identity with Δ6-desaturase from adult zebrafish (Genbank accessionnumber AW281238). A similar degree of amino acid (29.6%-28.7%) homologywas found with human Δ6-desaturase (Genbank accession number AF126799),Physcomitrella patens (moss) Δ6-desaturase (Genbank accession numberAJ222980), Brassica napus (canola) Δ8-sphingolipid desaturase (Genbankaccession number AJ224160), and human Δ5-desaturase (ATCC accessionnumber 203557, Genbank accession number AF199596). Since there was areasonable degree of amino acid homology to known desaturases, afull-length gene encoding a potential desaturase was sought to determineits activity when expressed in yeast.

To isolate the 3′ end of the gene, 10 pmol of primer RO936 (SEQ IDNO:23) (5′-GTCGGGCAAGGCGGAAAAGTACCTCAAGAG-3′) and vector primer RO899(SEQ ID NO:8) were combined in a reaction with 100 ng of purifiedplasmid from the T. aureum cDNA library in reaction volume of 100 μl inTaq PCR Master Mix (Qiagen, Valencia, Calif.). Thermocycling conditionswere as follows: an initial melt at 94° C. for 3 minutes followed by 30cycles of 94° C. for 1 minute, 60° C. for 1 minute, and 72° C. for 2minutes. This was followed by an extension step of 10 minutes at 72° C.Several bands, including the predicted size of 1.2 kb, were separated ona 1% agarose gel and purified as stated earlier. Also as describedearlier, the ends of the fragments were blunt ended, cloned into PCRBlunt and sequenced. Fragment #70-2 of approximately 1.2 kb wassequenced and contained an open reading frame and a stop codon, whichoverlapped fragment 30-9.

To isolate the 5′ end of the gene, RO937 (SEQ ID NO:24)(5′-AAACCTGTAGACAATGTGGAGGGGCGTGGG-3′) and RO 899 (SEQ ID NO:8) wereused in a 50 μl PCR reaction with Advantage-GC cDNA PCR kit (Clonetech,Palo Alto, Calif.), as per the manufacturer's protocol, with 100 ng ofpurified plasmid DNA from the library and 10 pmol of each primer. Thethermocycling conditions were as follows: An initial denaturation wascarried out at 94° C. for 1 minute, followed by 30 cycles of[denaturation at 94° C. for 30 seconds, annealing and extension 68° C.for 3 minutes], and a final extension cycle at 68° C. for 5 minutes. Aband of approximately 500 bp, in the range of the expected size, was gelpurified, blunt ended and cloned into PCR Blunt as previously described.Clone 95-2 contained an open reading frame with a start codon. Thisfragment also overlapped with clone 30-9, indicating that they wereindeed pieces of the same gene.

To isolate the full-length gene, primers were designed with restrictionsites 5′ and 3′ (underlined) with EcoRI and XhoI, respectively, asfollows: 5′ primer RO972 (SEQ ID NO:25)(5′-TACTTGAATTCATGGGACGCGGCGGCGAAGGTCAGGTGAAC-3′), 3′ primer RO949 (SEQID NO: 26) (5′-CTTATACTCGAGCTAAGCGGCCTTGGCCGCCGCCTGGCC-3′) and 3′ primerRO950 (SEQ ID NO:27) (5′-CTTATACTCGAGTAAATGGCTCGCGAGGCGAAGCGAGTGGC-3′).Two primers were used for the 3′ end of the gene in the initialisolation attempt since the primer RO949, containing the stop codon had66% GC content, while the alternate primer RO950, which was outside thestop codon, had only a 56% GC content. A 50 μl PCR reaction withRO972/RO949 and RO972/950 was performed with Advantage-GC cDNA PCR kit(Clonetech, Palo Alto, Calif.) under identical conditions noted in thepreceding paragraph. Only the primer set RO972/950 produced a band ofapproximately 1.6 kb. Use of genomic DNA as a template (under identicalconditions with 100 ng of target) also produced a similar-sized band.Fragments were separated on an agarose gel, gel purified, blunt-endedand cloned into PCR Blunt as previously described. Fragments wereevaluated by sequencing, and a number of clones were cut with EcoRI/XhoIto excise the full length gene, ligated to pYX242 EcoRI/XhoI which hadbeen treated with shrimp alkaline phosphatase (Roche, Indianapolis,Ind.) with the Rapid ligation kit (Roche, Indianapolis, Ind.). Clone99-3, designated pRTA4, contained the full length gene of 1317 by (SEQID NO:28, FIG. 6) and an open reading frame of 439 aa (SEQ IN NO: 29,FIG. 7). (The nucleotide sequence encoding the Δ5-desaturase wasdeposited with the ATCC, University Boulevard, Manassas, Va. 20110 underthe terms of the Budapest Treaty on Jan. 23, 2001 and was accordedaccession number PTA-2927.) This gene contained three histidine boxes atamino acid numbers 171-175, 208-212, and 376-380. The 5′-end of thegene, when translated, also shows homology to cytochrome b5.

Example 7 Expression of T. aureum Desaturase Gene in Baker's Yeast

The clone pRTA4 containing the full-length gene was transformed into theyeast host S. cerevisiae 334 and plated on selective media as describedin Example 4. The cultures were grown at 24° C. for 48 hours in minimalmedia lacking leucine with 50 μM of exogenous free fatty acid added as asubstrate as shown in Table 5. The only conversion of a substrate wasDGLA (20:3n-6) to ARA (20:4n-6). The conversion of 23.7% of the addedDGLA indicates that this gene encodes for a Δ5-desaturase.

Table 6 shows some of the fatty acids as a percentage of the lipidextracted from the yeast host. For Δ5-desaturase activity, there was nobackground (detection of ARA observed in the negative control containingthe yeast expression plasmid, PYX242.)

Example 8 Co-Expression of T. aureum Desaturase Gene with Elongases

The plasmid pRTA4 was co-transformed with an additional enzyme in thePUFA pathway, pRAE73-A3 which contains the human elongase gene in theyeast expression vector pYES2 as described in Example 4, andco-transformants were selected on minimal media lacking leucine anduracil.

Table 7 shows that when 100 μm of the substrate DGLA was added, that theΔ5-desaturase actively produced ARA, to which the elongase was able toadd two carbons to produce ADA. The percent conversion of T. aureumΔ5-desaturase, which consists of both ARA and ADA (products), was 16.7%,with no background observed from the negative control.

In view of the above results, T. aureum β5-desaturase is able to producea product in a heterologous expression system that can be used by anadditional heterologous enzyme in the PUFA biosynthetic pathway toproduce the expected PUFA.

Nutritional Compositions

The PUFAs described in the Detailed Description may be utilized invarious nutritional supplements, infant formulations, nutritionalsubstitutes and other nutritional solutions.

I. Infant Formulations

A. Isomil® Soy Formula with Iron:

Usage: As a beverage for infants, children and adults with an allergy orsensitivity to cows milk. A feeding for patients with disorders forwhich lactose should be avoided: lactase deficiency, lactose intoleranceand galactosemia.

Features:

-   -   Soy protein isolate to avoid symptoms of cow's-milk-protein        allergy or sensitivity.    -   Lactose-free formulation to avoid lactose-associated diarrhea.    -   Low osmolality (240 mOs/kg water) to reduce risk of osmotic        diarrhea.    -   Dual carbohydrates (corn syrup and sucrose) designed to    -    enhance carbohydrate absorption and reduce the risk of        exceeding the absorptive capacity of the damaged gut.    -   1.8 mg of Iron (as ferrous sulfate) per 100 Calories to help        prevent iron deficiency.    -   Recommended levels of vitamins and minerals.    -   Vegetable oils to provide recommended levels of essential fatty        acids.    -   Milk-white color, milk-like consistency and pleasant aroma.        Ingredients: (Pareve) 85% water, 4.9% corn syrup, 2.6% sugar        (sucrose), 2.1% soy oil, 1.9% soy protein isolate, 1.4% coconut        oil, 0.15% calcium citrate, 0.11% calcium phosphate tribasic,        potassium citrate, potassium phosphate monobasic, potassium        chloride, mono- and disglycerides, soy lecithin, carrageenan,        ascorbic acid, L-methionine, magnesium chloride, potassium        phosphate dibasic, sodium chloride, choline chloride, taurine,        ferrous sulfate, m-inositol, alpha-tocopheryl acetate, zinc        sulfate, L-carnitine, niacinamide, calcium pantothenate, cupric        sulfate, vitamin A palmitate, thiamine chloride hydrochloride,        riboflavin, pyridoxine hydrochloride, folic acid, manganese        sulfate, potassium iodide, phylloquinone, biotin, sodium        selenite, vitamin D3 and cyanocobalamin.        B. Isomil® DF Soy Formula for Diarrhea:        Usage: As a short-term feeding for the dietary management of        diarrhea in infants and toddlers.        Features:    -   First infant formula to contain added dietary fiber from soy        fiber specifically for diarrhea management.    -   Clinically shown to reduce the duration of loose, watery stools        during mild to severe diarrhea in infants.    -   Nutritionally complete to meet the nutritional needs of the        infant.    -   Soy protein isolate with added L-methionine meets or exceeds an        infant's requirement for all essential amino acids.    -   Lactose-free formulation to avoid lactose-associated diarrhea.    -   Low osmolality (240 mOsm/kg water) to reduce the risk of osmotic        diarrhea.    -   Dual carbohydrates (corn syrup and sucrose) designed to enhance        carbohydrate absorption and reduce the risk of exceeding the        absorptive capacity of the damaged gut.    -   Meets or exceeds the vitamin and mineral levels recommended by        the Committee on Nutrition of the American Academy of Pediatrics        and required by the Infant Formula Act.    -   1.8 mg of iron (as ferrous sulfate) per 100 Calories to help        prevent iron deficiency.    -   Vegetable oils to provide recommended levels of essential fatty        acids.        Ingredients: (Pareve) 86% water, 4.8% corn syrup, 2.5% sugar        (sucrose), 2.1% soy oil, 2.0% soy protein isolate, 1.4% coconut        oil, 0.77% soy fiber, 0.12% calcium citrate, 0.11% calcium        phosphate tribasic, 0.10% potassium citrate, potassium chloride,        potassium phosphate monobasic, mono and diglycerides, soy        lecithin, carrageenan, magnesium chloride, ascorbic acid,        L-methionine, potassium phosphate dibasic, sodium chloride,        choline chloride, taurine, ferrous sulfate, m-inositol,        alpha-tocopheryl acetate, zinc sulfate, L-carnitine,        niacinamide, calcium pantothenate, cupric sulfate, vitamin A        palmitate, thiamine chloride hydrochloride, riboflavin,        pyridoxine hydrochloride, folic acid, manganese sulfate,        potassium iodide, phylloquinone, biotin, sodium selenite,        vitamin D3 and cyanocobalamin.        C. Isomil® SF Sucrose-Free Soy Formula with Iron:        Usage: As a beverage for infants, children and adults with an        allergy or sensitivity to cow's-milk protein or an intolerance        to sucrose. A feeding for patients with disorders for which        lactose and sucrose should be avoided.        Features:    -   Soy protein isolate to avoid symptoms of cow's-milk-protein        allergy or sensitivity.    -   Lactose-free formulation to avoid lactose-associated diarrhea        (carbohydrate source is Polycose® Glucose Polymers).    -   Sucrose free for the patient who cannot tolerate sucrose.    -   Low osmolality (180 mOsm/kg water) to reduce risk of osmotic        diarrhea.    -   1.8 mg of iron (as ferrous sulfate) per 100 Calories to help        prevent iron deficiency.    -   Recommended levels of vitamins and minerals.    -   Vegetable oils to provide recommended levels of essential fatty        acids.    -   Milk-white color, milk-like consistency and pleasant aroma.        Ingredients: (Pareve) 75% water, 11.8% hydrolized cornstarch,        4.1% soy oil, 4.1% soy protein isolate, 2.8% coconut oil, 1.0%        modified cornstarch, 0.38% calcium phosphate tribasic, 0.17%        potassium citrate, 0.13% potassium chloride, mono- and        diglycerides, soy lecithin, magnesium chloride, abscorbic acid,        L-methionine, calcium carbonate, sodium chloride, choline        chloride, carrageenan, taurine, ferrous sulfate, m-inositol,        alpha-tocopheryl acetate, zinc sulfate, L-carnitine,        niacinamide, calcium pantothenate, cupric sulfate, vitamin A        palmitate, thiamine chloride hydrochloride, riboflavin,        pyridoxine hydrochloride, folic acid, manganese sulfate,        potassium iodide, phylloquinone, biotin, sodium selenite,        vitamin D3 and cyanocobalamin.        D. Isomil® 20 Soy Formula with Iron Ready to Feed, 20 Cal/fl        oz.:        Usage: When a soy feeding is desired.        Ingredients: (Pareve) 85% water, 4.9% corn syrup, 2.6%        sugar(sucrose), 2.1% soy oil, 1.9% soy protein isolate, 1.4%        coconut oil, 0.15% calcium citrate, 0.11% calcium phosphate        tribasic, potassium citrate, potassium phosphate monobasic,        potassium chloride, mono- and diglycerides, soy lecithin,        carrageenan, abscorbic acid, L-methionine, magnesium chloride,        potassium phosphate dibasic, sodium chloride, choline chloride,        taurine, ferrous sulfate, m-inositol, alpha-tocopheryl acetate,        zinc sulfate, L-carnitine, niacinamide, calcium pantothenate,        cupric sulfate, vitamin A palmitate, thiamine chloride        hydrochloride, riboflavin, pyridoxine hydrochloride, folic acid,        manganese sulfate, potassium iodide, phylloquinone, biotin,        sodium selenite, vitamin D3 and cyanocobalamin.        E. Similac® Infant Formula:        Usage: When an infant formula is needed: if the decision is made        to discontinue breastfeeding before age 1 year, if a supplement        to breastfeeding is needed or as a routine feeding if        breastfeeding is not adopted.        Features:    -   Protein of appropriate quality and quantity for good growth;        heat-denatured, which reduces the risk of milk-associated        enteric blood loss.    -   Fat from a blend of vegetable oils (doubly homogenized),        providing essential linoleic acid that is easily absorbed.    -   Carbohydrate as lactose in proportion similar to that of human        milk.    -   Low renal solute load to minimize stress on developing organs.    -   Powder, Concentrated Liquid and Ready To Feed forms.        Ingredients: (-D) Water, nonfat milk, lactose, soy oil, coconut        oil, mono- and diglycerides, soy lecithin, abscorbic acid,        carrageenan, choline chloride, taurine, m-inositol,        alpha-tocopheryl acetate, zinc sulfate, niacinamide, ferrous        sulfate, calcium pantothenate, cupric sulfate, vitamin A        palmitate, thiamine chloride hydrochloride, riboflavin,        pyridoxine hydrochloride, folic acid, manganese sulfate,        phylloquinone, biotin, sodium selenite, vitamin D3 and        cyanocobalamin.        F. Similac® NeoCare Premature Infant Formula with Iron:        Usage: For premature infants' special nutritional needs after        hospital discharge. Similac NeoCare is a nutritionally complete        formula developed to provide premature infants with extra        calories, protein, vitamins and minerals needed to promote        catch-up growth and support development.        Features:    -   Reduces the need for caloric and vitamin supplementation. More        calories (22 Cal/fl. oz) than standard term formulas (20 Cal/fl        oz).    -   Highly absorbed fat blend, with medium-chain triglycerides    -    (MCToil) to help meet the special digestive needs of premature        infants.    -   Higher levels of protein, vitamins and minerals per 100 calories        to extend the nutritional support initiated in-hospital.    -   More calcium and phosphorus for improved bone mineralization.        Ingredients: -D Corn syrup solids, nonfat milk, lactose, whey        protein concentrate, soy oil, high-oleic safflower oil,        fractionated coconut oil (medium chain triglycerides), coconut        oil, potassium citrate, calcium phosphate tribasic, calcium        carbonate, ascorbic acid, magnesium chloride, potassium        chloride, sodium chloride, taurine, ferrous sulfate, m-inositol,        choline chloride, ascorbyl palmitate, L-carnitine,        alpha-tocopheryl acetate, zinc sulfate, niacinamide, mixed        tocopherols, sodium citrate, calcium pantothenate, cupric        sulfate, thiamine chloride hydrochloride, vitamin A palmitate,        beta carotene, riboflavin, pyridoxine hydrochloride, folic acid,        manganese sulfate, phylloquinone, biotin, sodium selenite,        vitamin D3 and cyanocobalamin.        G. Similac Natural Care Low-Iron Human Milk Fortifier Ready to        Use, 24 Cal/fl. oz.:

Usage: Designed to be mixed with human milk or to be fed alternativelywith human milk to low-birth-weight infants.

Ingredients: -D Water, nonfat milk, hydrolyzed cornstarch, lactose,fractionated coconut oil (medium-chain triglycerides), whey proteinconcentrate, soy oil, coconut oil, calcium phosphate tribasic, potassiumcitrate, magnesium chloride, sodium citrate, ascorbic acid, calciumcarbonate, mono and diglycerides, soy lecithin, carrageenan, cholinechloride, m-inositol, taurine, niacinamide, L-carnitine, alphatocopheryl acetate, zinc sulfate, potassium chloride, calciumpantothenate, ferrous sulfate, cupric sulfate, riboflavin, vitamin Apalmitate, thiamine chloride hydrochloride, pyridoxine hydrochloride,biotin, folic acid, manganese sulfate, phylloquinone, vitamin D3, sodiumselenite and cyanocobalamin.

Various PUFAs of this invention can be substituted and/or added to theinfant formulae described above and to other infant formulae known tothose in the art.

II. Nutritional Formulations

A. ENSURE®

Usage: ENSURE is a low-residue liquid food designed primarily as an oralnutritional supplement to be used with or between meals or, inappropriate amounts, as a meal replacement. ENSURE is lactose- andgluten-free, and is suitable for use in modified diets, includinglow-cholesterol diets. Although it is primarily an oral supplement, itcan be fed by tube.Patient Conditions:

-   -   For patients on modified diets    -   For elderly patients at nutrition risk    -   For patients with involuntary weight loss    -   For patients recovering from illness or surgery    -   For patients who need a low-residue diet        Ingredients: -D Water, Sugar (Sucrose), Maltodextrin (Corn),        Calcium and Sodium Caseinates, High-Oleic Safflower Oil, Soy        Protein Isolate, Soy Oil, Canola Oil, Potassium Citrate, Calcium        Phosphate Tribasic, Sodium Citrate, Magnesium Chloride,        Magnesium Phosphate Dibasic, Artificial Flavor, Sodium Chloride,        Soy Lecithin, Choline Chloride, Ascorbic Acid, Carrageenan, Zinc        Sulfate, Ferrous Sulfate, Alpha-Tocopheryl Acetate, Gellan Gum,        Niacinamide, Calcium Pantothenate, Manganese Sulfate, Cupric        Sulfate, Vitamin A Palmitate, Thiamine Chloride Hydrochloride,        Pyridoxine Hydrochloride, Riboflavin, Folic Acid, Sodium        Molybdate, Chromium Chloride, Biotin, Potassium Iodide, Sodium        Selenate.        B. ENSURE®BARS:        Usage: ENSURE BARS are complete, balanced nutrition for        supplemental use between or with meals. They provide a        delicious, nutrient-rich alternative to other snacks. ENSURE        BARS contain <1 g lactose/bar, and Chocolate Fudge Brownie        flavor is gluten-free. (Honey Graham Crunch Flavor Contains        Gluten.)        Patient Conditions:    -   For patients who need extra calories, protein, vitamins and        minerals.    -   Especially useful for people who do not take in enough calories        and nutrients.    -   For people who have the ability to chew and swallow    -   Not to be used by anyone with a peanut allergy or any type of        allergy to nuts.        Ingredients: Honey Graham Crunch—High-Fructose Corn Syrup, Soy        Protein Isolate, Brown Sugar, Honey, Maltodextrin (Corn), Crisp        Rice (Milled Rice, Sugar [Sucrose], Salt [Sodium Chloride] and        Malt), Oat Bran, Partially Hydrogenated Cottonseed and Soy Oils,        Soy Polysaccharide, Glycerine, Whey Protein Concentrate,        Polydextrose, Fructose, Calcium Caseinate, Cocoa Powder,        Artificial Flavors, Canola Oil, High-Oleic Safflower Oil, Nonfat        Dry Milk, Whey Powder, Soy Lecithin and Corn Oil. Manufactured        in a facility that processes nuts.        Vitamins and Minerals: Calcium Phosphate Tribasic, Potassium        Phosphate Dibasic, Magnesium Oxide, Salt (Sodium Chloride),        Potassium Chloride, Ascorbic Acid, Ferric Orthophosphate,        Alpha-Tocopheryl Acetate, Niacinamide, Zinc Oxide, Calcium        Pantothenate, Copper Gluconate, Manganese Sulfate, Riboflavin,        Beta Carotene, Pyridoxine Hydrochloride, Thiamine Mononitrate,        Folic Acid, Biotin, Chromium Chloride, Potassium Iodide, Sodium        Selenate, Sodium Molybdate, Phylloquinone, Vitamin D3 and        Cyanocobalamin.        Protein: Honey Graham Crunch—The protein source is a blend of        soy protein isolate and milk proteins.

Soy protein isolate 74% Milk proteins 26%Fat: Honey Graham Crunch—The fat source is a blend of partiallyhydrogenated cottonseed and soybean, canola, high oleic safflower, oils,and soy lecithin.

Partially hydrogenated cottonseed and soybean oil 76%  Canola oil 8%High-oleic safflower oil 8% Corn oil 4% Soy lecithin 4%Carbohydrate: Honey Graham Crunch—The carbohydrate source is acombination of high-fructose corn syrup, brown sugar, maltodextrin,honey, crisp rice, glycerine, soy polysaccharide, and oat bran.

High-fructose corn syrup 24% Brown sugar 21% Maltodextrin 12% Honey 11%Crisp rice  9% Glycerine  9% Soy Polysaccharide  7% Oat bran  7%C. ENSURE® HIGH PROTEIN:Usage: ENSURE HIGH PROTEIN is a concentrated, high-protein liquid fooddesigned for people who require additional calories, protein, vitamins,and minerals in their diets. It can be used as an oral nutritionalsupplement with or between meals or, in appropriate amounts, as a mealreplacement. ENSURE HIGH PROTEIN is lactose- and gluten-free, and issuitable for use by people recovering from general surgery or hipfractures and by patients at risk for pressure ulcers.Patient Conditions:

-   -   For patients who require additional calories, protein, vitamins,        and minerals, such as patients recovering from general surgery        or hip fractures, patients at risk for pressure ulcers, and        patients on low-cholesterol diets.        Features:    -   Low in saturated fat    -   Contains 6 g of total fat and <5 mg of cholesterol per serving    -   Rich, creamy taste    -   Excellent source of protein, calcium, and other essential        vitamins and minerals    -   For low-cholesterol diets    -   Lactose-free, easily digested        Ingredients:        Vanilla Supreme: -D Water, Sugar (Sucrose), Maltodextrin (Corn),        Calcium and Sodium Caseinates, High-Oleic Safflower Oil, Soy        Protein Isolate, Soy Oil, Canola Oil, Potassium Citrate, Calcium        Phosphate Tribasic, Sodium Citrate, Magnesium Chloride,        Magnesium Phosphate Dibasic, Artificial Flavor, Sodium Chloride,        Soy Lecithin, Choline Chloride, Ascorbic Acid, Carrageenan, Zinc        Sulfate, Ferrous Sulfate, Alpha-Tocopheryl Acetate, Gellan Gum,        Niacinamide, Calcium Pantothenate, Manganese Sulfate, Cupric        Sulfate, Vitamin A Palmitate, Thiamine Chloride Hydrochloride,        Pyridoxine Hydrochloride, Riboflavin, Folic Acid, Sodium        Molybdate, Chromium Chloride, Biotin, Potassium Iodide, Sodium        Selenate, Phylloquinone, Vitamin D3 and Cyanocobalamin.        Protein:

The protein source is a blend of two high-biologic-value proteins:casein and soy.

Sodium and calcium caseinates 85% Soy protein isolate 15%Fat:

The fat source is a blend of three oils: high-oleic safflower, canola,and soy.

High-oleic safflower oil 40% Canola oil 30% Soy oil 30%The level of fat in ENSURE HIGH PROTEIN meets American Heart Association(AHA) guidelines. The 6 grams of fat in ENSURE HIGH PROTEIN represent24% of the total calories, with 2.6% of the fat being from saturatedfatty acids and 7.9% from polyunsaturated fatty acids. These values arewithin the AHA guidelines of <30% of total calories from fat, <10% ofthe calories from saturated fatty acids, and <10% of total calories frompolyunsaturated fatty acids.Carbohydrate:

ENSURE HIGH PROTEIN contains a combination of maltodextrin and sucrose.The mild sweetness and flavor variety (vanilla supreme, chocolate royal,wild berry, and banana), plus VARI-FLAVORS® Flavor Pacs in pecan,cherry, strawberry, lemon, and orange, help to prevent flavor fatigueand aid in patient compliance.

Vanilla and Other Nonchocolate Flavors:

Sucrose 60% Maltodextrin 40%Chocolate:

Sucrose 70% Maltodextrin 30%D. Ensured LightUsage: ENSURE LIGHT is a low-fat liquid food designed for use as an oralnutritional supplement with or between meals. ENSURE LIGHT is lactose-and gluten-free, and is suitable for use in modified diets, includinglow-cholesterol diets.Patient Conditions:

-   -   For normal-weight or overweight patients who need extra        nutrition in a supplement that contains 50% less fat and 20%        fewer calories than ENSURE.    -   For healthy adults who do not eat right and need extra        nutrition.        Features:    -   Low in fat and saturated fat    -   Contains 3 g of total fat per serving and <5 mg cholesterol    -   Rich, creamy taste    -   Excellent source of calcium and other essential vitamins and        minerals    -   For low-cholesterol diets    -   Lactose-free, easily digested        Ingredients:        French Vanilla: -D Water, Maltodextrin (Corn), Sugar (Sucrose),        Calcium Caseinate, High-Oleic Safflower Oil, Canola Oil,        Magnesium Chloride, Sodium Citrate, Potassium Citrate, Potassium        Phosphate Dibasic, Magnesium Phosphate Dibasic, Natural and        Artificial Flavor, Calcium Phosphate Tribasic, Cellulose Gel,        Choline Chloride, Soy Lecithin, Carrageenan, Salt (Sodium        Chloride), Ascorbic Acid, Cellulose Gum, Ferrous Sulfate,        Alpha-Tocopheryl Acetate, Zinc Sulfate, Niacinamide, Manganese        Sulfate, Calcium Pantothenate, Cupric Sulfate, Thiamine Chloride        Hydrochloride, Vitamin A Palmitate, Pyridoxine Hydrochloride,        Riboflavin, Chromium Chloride, Folic Acid, Sodium Molybdate,        Biotin, Potassium Iodide, Sodium Selenate, Phylloquinone,        Vitamin D3 and Cyanocobalamin.        Protein:        The protein source is calcium caseinate.

Calcium caseinate 100%Fat:The fat source is a blend of two oils: high-oleic safflower and canola.

High-oleic safflower oil 70% Canola oil 30%The level of fat in ENSURE LIGHT meets American Heart Association (AHA)guidelines. The 3 grams of fat in ENSURE LIGHT represent 13.5% of thetotal calories, with 1.4% of the fat being from saturated fatty acidsand 2.6% from polyunsaturated fatty acids. These values are within theAHA guidelines of <30% of total calories from fat, <10% of the, caloriesfrom saturated fatty acids, and <10% of total calories frompolyunsaturated fatty acids.Carbohydrate:ENSURE LIGHT contains a combination of maltodextrin and sucrose. Thechocolate flavor contains corn syrup as well. The mild sweetness andflavor variety (French vanilla, chocolate supreme, strawberry swirl),plus VARI-FLAVORS® Flavor Pacs in pecan, cherry, strawberry, lemon, andorange, help to prevent flavor fatigue and aid in patient compliance.Vanilla and Other Nonchocolate Flavors:

Sucrose 51% Maltodextrin 49%Chocolate:

Sucrose 47.0% Corn Syrup 26.5% Maltodextrin 26.5%Vitamins and Minerals:An 8-fl-oz serving of ENSURE LIGHT provides at least 25% of the RDIs for24 key vitamins and minerals.Caffeine:

Chocolate flavor contains 2.1 mg caffeine/8 fl oz.

E. ENSURE PLUS®

Usage: ENSURE PLUS is a high-calorie, low-residue liquid food for usewhen extra calories and nutrients, but a normal concentration ofprotein, are needed. It is designed primarily as an oral nutritionalsupplement to be used

with or between meals or, in appropriate amounts, as a meal replacement.ENSURE PLUS is lactose- and gluten-free. Although it is primarily anoral nutritional supplement, it can be fed by tube.

Patient Conditions:

-   -   For patients who require extra calories and nutrients, but a        normal concentration of protein, in a limited volume.    -   For patients who need to gain or maintain healthy weight.        Features:    -   Rich, creamy taste    -   Good source of essential vitamins and minerals        Ingredients:        Vanilla: -D Water, Corn Syrup, Maltodextrin (Corn), Corn Oil,        Sodium and Calcium Caseinates, Sugar (Sucrose), Soy Protein        Isolate, Magnesium Chloride, Potassium Citrate, Calcium        Phosphate Tribasic, Soy Lecithin, Natural and Artificial Flavor,        Sodium Citrate, Potassium Chloride, Choline Chloride, Ascorbic        Acid, Carrageenan, Zinc Sulfate, Ferrous Sulfate,        Alpha-Tocopheryl Acetate, Niacinamide, Calcium Pantothenate,        Manganese Sulfate, Cupric Sulfate, Thiamine Chloride        Hydrochloride, Pyridoxine Hydrochloride, Riboflavin, Vitamin A        Palmitate, Folic Acid, Biotin, Chromium Chloride, Sodium        Molybdate, Potassium Iodide, Sodium Selenite, Phylloquinone,        Cyanocobalamin and Vitamin D3.        Protein:

The protein source is a blend of two high-biologic-value proteins:casein and soy.

Sodium and calcium caseinates 84% Soy protein isolate 16%Fat:

The fat source is corn oil.

Corn oil 100%Carbohydrate:

ENSURE PLUS contains a combination of maltodextrin and sucrose. The mildsweetness and flavor variety (vanilla, chocolate, strawberry, coffee,buffer pecan, and eggnog), plus VARI-FLAVORS® Flavor Pacs in pecan,cherry, strawberry, lemon, and orange, help to prevent flavor fatigueand aid in patient compliance.

Vanilla, Strawberry, Butter Pecan, and Coffee Flavors:

Corn Syrup 39% Maltodextrin 38% Sucrose 23%Chocolate and Eggnog Flavors:

Corn Syrup 36% Maltodextrin 34% Sucrose 30%Vitamins and Minerals:

An 8-fl-oz serving of ENSURE PLUS provides at least 15% of the RDIs for25 key Vitamins and minerals.

Caffeine:

Chocolate flavor contains 3.1 mg Caffeine/8 fl oz. Coffee flavorcontains a trace amount of caffeine.

F. ENSURE PLUS® HN

Usage: ENSURE PLUS HN is a nutritionally complete high-calorie,high-nitrogen liquid food designed for people with higher calorie andprotein needs or limited volume tolerance. It may be used for oralsupplementation or for total nutritional support by tube. ENSURE PLUS HNis lactose- and gluten-free.Patient Conditions:

-   -   For patients with increased calorie and protein needs, such as        following surgery or injury.    -   For patients with limited volume tolerance and early satiety.        Features:    -   For supplemental or total nutrition    -   For oral or tube feeding    -   1.5 CaVmL,    -   High nitrogen    -   Calorically dense        Ingredients:        Vanilla: -D Water, Maltodextrin (Corn), Sodium and Calcium        Caseinates, Corn Oil, Sugar (Sucrose), Soy Protein Isolate,        Magnesium Chloride, Potassium Citrate, Calcium Phosphate        Tribasic, Soy Lecithin, Natural and Artificial Flavor, Sodium        Citrate, Choline Chloride, Ascorbic Acid, Taurine, L-Carnitine,        Zinc Sulfate, Ferrous Sulfate, Alpha-Tocopheryl Acetate,        Niacinamide, Carrageenan, Calcium Pantothenate, Manganese        Sulfate, Cupric Sulfate, Thiamine Chloride Hydrochloride,        Pyridoxine Hydrochloride, Riboflavin, Vitamin A Palmitate, Folic        Acid, Biotin, Chromium Chloride, Sodium Molybdate, Potassium        Iodide, Sodium Selenite, Phylloquinone, Cyanocobalamin and        Vitamin D3.        G. ENSURE® Powder:        Usage: ENSURE POWDER (reconstituted with water) is a low-residue        liquid food designed primarily as an oral nutritional supplement        to be used with or between meals. ENSURE POWDER is lactose- and        gluten-free, and is suitable for use in modified diets,        including low-cholesterol diets.        Patient Conditions:    -   For patients on modified diets    -   For elderly patients at nutrition risk    -   For patients recovering from illness/surgery    -   For patients who need a low-residue diet        Features:    -   Convenient, easy to mix    -   Low in saturated fat    -   Contains 9 g of total fat and <5 mg of cholesterol per serving    -   High in vitamins and minerals    -   For low-cholesterol diets    -   Lactose-free, easily digested        Ingredients: -D Corn Syrup, Maltodextrin (Corn), Sugar        (Sucrose), Corn Oil, Sodium and Calcium Caseinates, Soy Protein        Isolate, Artificial Flavor, Potassium Citrate, Magnesium        Chloride, Sodium Citrate, Calcium Phosphate Tribasic, Potassium        Chloride, Soy Lecithin, Ascorbic Acid, Choline Chloride, Zinc        Sulfate, Ferrous Sulfate, Alpha-Tocopheryl Acetate, Niacinamide,        Calcium Pantothenate, Manganese Sulfate, Thiamine Chloride        Hydrochloride, Cupric Sulfate, Pyridoxine Hydrochloride,        Riboflavin, Vitamin A Palmitate, Folic Acid, Biotin, Sodium        Molybdate, Chromium Chloride, Potassium Iodide, Sodium Selenate,        Phylloquinone, Vitamin D3 and Cyanocobalamin.        Protein:        The protein source is a blend of two high-biologic-value        proteins: casein and soy.

Sodium and calcium caseinates 84% Soy protein isolate 16%Fat:

The fat source is corn oil.

Corn oil 100%Carbohydrate:

ENSURE POWDER contains a combination of corn syrup, maltodextrin, andsucrose. The mild sweetness of ENSURE POWDER, plus VARI-FLAVORS® FlavorPacs in pecan, cherry, strawberry, lemon, and orange, helps to preventflavor fatigue and aid in patient compliance.

Vanilla:

Corn Syrup 35% Maltodextrin 35% Sucrose 30%H. ENSURE® PUDDINGUsage: ENSURE PUDDING is a nutrient-dense supplement providing balancednutrition in a nonliquid form to be used with or between meals. It isappropriate for consistency-modified diets (e.g., soft, pureed, or fullliquid) or for people with swallowing impairments. ENSURE PUDDING isgluten-free.Patient Conditions:

-   -   For patients on consistency-modified diets (e.g., soft, pureed,        or full liquid)    -   For patients with swallowing impairments        Features:    -   Rich and creamy, good taste    -   Good source of essential vitamins and minerals    -   Convenient-needs no refrigeration    -   Gluten-free        Nutrient Profile per 5 oz: Calories 250, Protein 10.9%, Total        Fat 34.9%, Carbohydrate 54.2%        Ingredients:        Vanilla: -D Nonfat Milk, Water, Sugar (Sucrose), Partially        Hydrogenated Soybean Oil, Modified Food Starch, Magnesium        Sulfate, Sodium Stearoyl Lactylate, Sodium Phosphate Dibasic,        Artificial Flavor, Ascorbic Acid, Zinc Sulfate, Ferrous Sulfate,        Alpha-Tocopheryl Acetate, Choline Chloride, Niacinamide,        Manganese Sulfate, Calcium Pantothenate, FD&C Yellow #5,        Potassium Citrate, Cupric Sulfate, Vitamin A Palmitate, Thiamine        Chloride Hydrochloride, Pyridoxine Hydrochloride, Riboflavin,        FD&C Yellow #6, Folic Acid, Biotin, Phylloquinone, Vitamin D3        and Cyanocobalamin.        Protein:

The protein source is nonfat milk.

Nonfat milk 100%Fat:

The fat source is hydrogenated soybean oil.

Hydrogenated soybean oil 100%Carbohydrate:

ENSURE PUDDING contains a combination of sucrose and modified foodstarch. The mild sweetness and flavor variety (vanilla, chocolate,butterscotch, and tapioca) help prevent flavor fatigue. The productcontains 9.2 grams of lactose per serving.

Vanilla and Other Nonchocolate Flavors:

Sucrose 56% Lactose 27% Modified food starch 17%Chocolate:

Sucrose 58% Lactose 26% Modified food starch 16%I. ENSURE® WITH FIBER:

Usage: ENSURE WITH FIBER is a fiber-containing, nutritionally completeliquid food designed for people who can benefit from increased dietaryfiber and nutrients. ENSURE WITH FIBER is suitable for people who do notrequire a low-residue diet. It can be fed orally or by tube, and can beused as a nutritional supplement to a regular diet or, in appropriateamounts, as a meal replacement. ENSURE WITH FIBER is lactose- andgluten-free, and is suitable for use in modified diets, includinglow-cholesterol diets.

Patient Conditions:

-   -   For patients who can benefit from increased dietary fiber and        nutrients        Features:    -   New advanced formula-low in saturated fat, higher in vitamins        and minerals    -   Contains 6 g of total fat and <5 mg of cholesterol per serving    -   Rich, creamy taste    -   Good source of fiber    -   Excellent source of essential vitamins and minerals    -   For low-cholesterol diets    -   Lactose- and gluten-free        Ingredients:        Vanilla: -D Water; Maltodextrin (Corn), Sugar (Sucrose), Sodium        and Calcium Caseinates, Oat Fiber, High-Oleic Safflower Oil,        Canola Oil, Soy Protein Isolate, Corn Oil, Soy Fiber, Calcium        Phosphate Tribasic, Magnesium Chloride, Potassium Citrate,        Cellulose Gel, Soy Lecithin, Potassium Phosphate Dibasic, Sodium        Citrate, Natural and Artificial Flavors, Choline Chloride,        Magnesium Phosphate, Ascorbic Acid, Cellulose Gum, Potassium        Chloride, Carrageenan, Ferrous Sulfate, Alpha-Tocopheryl        Acetate, Zinc Sulfate, Niacinamide, Manganese Sulfate, Calcium        Pantothenate, Cupric Sulfate, Vitamin A Palmitate, Thiamine        Chloride Hydrochloride, Pyridoxine Hydrochloride, Riboflavin,        Folic Acid, Chromium Chloride, Biotin, Sodium Molybdate,        Potassium Iodide, Sodium Selenate, Phylloquinone, Vitamin D3 and        Cyanocobalamin.        Protein:

The protein source is a blend of two high-biologic-value proteins-caseinand soy.

Sodium and calcium caseinates 80% Soy protein isolate 20%Fat:

The fat source is a blend of three oils: high-oleic safflower, canola,and corn.

High-oleic safflower oil 40% Canola oil 40% Corn oil 20%The level of fat in ENSURE WITH FIBER meets American Heart Association(AHA) guidelines. The 6 grams of fat in ENSURE WITH FIBER represent 22%of the total calories, with 2.01% of the fat being from saturated fattyacids and 6.7% from polyunsaturated fatty acids. These values are withinthe AHA guidelines of <30% of total calories from fat, <10% of thecalories from saturated fatty acids, and <10% of total calories frompolyunsaturated fatty acids.Carbohydrate:

ENSURE WITH FIBER contains a combination of maltodextrin and sucrose.The mild sweetness and flavor variety (vanilla, chocolate, and butterpecan), plus VARI-FLAVORS® Flavor Pacs in pecan, cherry, strawberry,lemon, and orange, help to prevent flavor fatigue and aid in patientcompliance.

Vanilla and Other Nonchocolate Flavors:

Maltodextrin 66% Sucrose 25% Oat Fiber  7% Soy Fiber  2%Chocolate:

Maltodextrin 55% Sucrose 36% Oat Fiber  7% Soy Fiber  2%Fiber:

The fiber blend used in ENSURE WITH FIBER consists of oat fiber and soypolysaccharide. This blend results in approximately 4 grams of totaldietary fiber per 8-fl. oz can. The ratio of insoluble to soluble fiberis 95:5.

The various nutritional supplements described above and known to othersof skill in the art can be substituted and/or supplemented with thePUFAs produced in accordance with the present invention.

J. Oxepa™ Nutritional Product

Oxepa is a low-carbohydrate, calorically dense, enteral nutritionalproduct designed for the dietary management of patients with or at riskfor ARDS. It has a unique combination of ingredients, including apatented oil blend containing eicosapentaenoic acid (EPA from fish oil),γ-linolenic acid (GLA from borage oil), and elevated antioxidant levels.

Caloric Distribution:

Caloric density is high at 1.5 Cal/mL (355 Cal/8 fl oz), to minimize thevolume required to meet energy needs.

The distribution of Calories in Oxepa is shown in Table A.

TABLE A Caloric Distribution of Oxepa per 8 fl oz. per liter % of CalCalories 355 1,500 — Fat (g) 22.2 93.7 55.2 Carbohydrate (g) 25 105.528.1 Protein (g) 14.8 62.5 16.7 Water (g) 186 785 —Fat:

-   -   Oxepa contains 22.2 g of fat per 8-fl oz serving (93.7 g/L).    -   The fat source is an oil blend of 31.8% canola oil, 25%        medium-chain triglycerides (MCTs), 20% borage oil, 20% fish oil,        and 3.2% soy lecithin. The typical fatty acid profile of Oxepa        is shown in Table B.    -   Oxepa provides a balanced amount of polyunsaturated,        monounsaturated, and saturated fatty acids, as shown in Table        VI.    -   Medium-chain triglycerides (MCTs)—25% of the fat blend—aid        gastric emptying because they are absorbed by the intestinal        tract without emulsification by bile acids.        The various fatty acid components of Oxepa™ nutritional product        can be substituted and/or supplemented with the PUFAs produced        in accordance with this invention.

TABLE B Typical Fatty Acid Profile Fatty Acids % Total g/8 fl oz* 9/L*Caproic (6:0) 0.2 0.04 0.18 Caprylic (8:0) 14.69 3.1 13.07 Capric (10:0)11.06 2.33 9.87 Palmitic (16:0) 5.59 1.18 4.98 Palmitoleic 1.82 0.381.62 Stearic 1.94 0.39 1.64 Oleic 24.44 5.16 21.75 Linoleic 16.28 3.4414.49 α-Linolenic 3.47 0.73 3.09 γ-Linolenic 4.82 1.02 4.29Eicosapentaenoic 5.11 1.08 4.55 n-3-Docosapentaenoic 0.55 0.12 0.49Docosahexaenoic 2.27 0.48 2.02 Others 7.55 1.52 6.72Fatty acids equal approximately 95% of total fat.

TABLE C Fat Profile of Oxepa. % of total calories from fat 55.2Polyunsaturated fatty acids 31.44 g/L Monounsaturated fatty acids 25.53g/L Saturated fatty acids 32.38 g/L n-6 to n-3 ratio 1.75:1 Cholesterol9.49 mg/8 fl oz 40.1 mg/LCarbohydrate:

-   -   The carbohydrate content is 25.0 g per 8-fl-oz serving (105.5        g/L).    -   The carbohydrate sources are 45% maltodextrin (a complex        carbohydrate) and 55% sucrose (a simple sugar), both of which        are readily digested and absorbed.    -   The high-fat and low-carbohydrate content of Oxepa is designed        to minimize carbon dioxide (C02) production. High C02 levels can        complicate weaning in ventilator-dependent patients. The low        level of carbohydrate also may be useful for those patients who        have developed stress-induced hyperglycemia.    -   Oxepa is lactose-free.

Dietary carbohydrate, the amino acids from protein, and the glycerolmoiety of fats can be converted to glucose within the body. Throughoutthis process, the carbohydrate requirements of glucose-dependent tissues(such as the central nervous system and red blood cells) are met.However, a diet free of carbohydrates can lead to ketosis, excessivecatabolism of tissue protein, and loss of fluid and electrolytes. Theseeffects can be prevented by daily ingestion of 50 to 100 g of digestiblecarbohydrate, if caloric intake is adequate. The carbohydrate level inOxepa is also sufficient to minimize gluconeogenesis, if energy needsare being met.

Protein:

-   -   Oxepa contains 14.8 g of protein per 8-fl-oz serving (62.5 g/L).    -   The total calorie/nitrogen ratio (150:1) meets the need of        stressed patients.    -   Oxepa provides enough protein to promote anabolism and the        maintenance of lean body mass without precipitating respiratory        problems. High protein intakes are a concern in patients with        respiratory insufficiency. Although    -    protein has little effect on C02 production, a high protein        diet will increase ventilatory drive.    -   The protein sources of Oxepa are 86.8% sodium caseinate and        13.2% calcium caseinate.    -   The amino acid profile of the protein system in Oxepa meets or        surpasses the standard for high quality protein set by the        National Academy of Sciences.        * Oxepa is gluten-free.

1. An isolated nucleic acid molecule comprising a nucleotide sequencehaving at least 95% sequence identity to SEQ ID NO:19, wherein saidnucleotide sequence encodes a functionally active Δ5-desaturase.
 2. Theisolated nucleic acid molecule of claim 1, wherein said molecule encodesa functionally active desaturase which utilizes a polyunsaturated fattyacid as a substrate.
 3. The isolated nucleic acid molecule of claim 1,wherein said molecule is derived from a fungus.
 4. The isolated nucleicacid molecule of claim 3, wherein said fungus is Saprolegnia diclina. 5.A method of producing a desaturase in a host cell in vitro comprisingthe steps of: a) isolating a nucleic acid molecule comprising anucleotide sequence having at least 95% sequence identity to SEQ IDNO:19, wherein said nucleotide sequence encodes a functionally activeΔ5-desaturase; b) constructing a vector comprising: i) said isolatednucleotide sequence operably linked to ii) a regulatory sequence; c)introducing said vector into a host cell in vitro for a time and underconditions sufficient for expression of said desaturase.
 6. A vectorcomprising a nucleotide sequence having at least 95% sequence identityto SEQ ID NO:19 operably linked to a regulatory sequence, wherein saidnucleotide sequence encodes a functionally active Δ5-desaturase.
 7. Ahost cell comprising the vector of claim
 6. 8. The host cell of claim 7,wherein said host cell is a prokaryotic cell or a eukaryotic cell. 9.The host cell of claim 8, wherein said eukaryotic cell is selected fromthe group consisting of an insect cell, a plant cell, and a fungal cell.10. The host cell of claim 9, wherein the fungal cell is selected fromthe group consisting of Saccharomyces cerevisiae, Saccharomycescarlsbergensis, Candida spp., Lipomyces starkey, Yarrowia lipolytica,Kluyveromyces spp., Hansenula spp., Trichoderma spp., and Pichia spp.11. The host cell of claim 8, wherein said prokaryotic cell is selectedfrom the group consisting of E. coli, Cyanobacteria, and B. subtilis.12. A plant cell, plant or plant tissue comprising a vector comprising:a) a nucleotide sequence comprising SEQ ID NO:19 operably linked to b) apromoter, wherein expression of said nucleotide sequence of said vectorresults in production of a polyunsaturated fatty acid by said plant cellor tissue.
 13. The plant cell, plant, plant seed, or plant tissue ofclaim 12 wherein said polyunsaturated fatty acid is selected from thegroup consisting of AA or EPA.
 14. A method for producing apolyunsaturated fatty acid comprising the steps of: a) isolating anucleic acid molecule comprising a nucleotide sequence having at least95% sequence identity to SEQ ID NO:19, wherein said nucleotide sequenceencodes a functionally active Δ5-desaturase; b) constructing a vectorcomprising said isolated nucleic acid molecule; c) introducing saidvector into a host cell for a time and under conditions sufficient forexpression of Δ5-desaturase enzyme, wherein said host cell is aprokaryotic cell or a eukaryotic cell, wherein said eukaryotic cell isselected from the group consisting of an insect cell, a plant cell and afungal cell; and d) exposing said expressed Δ5-desaturase enzyme to asubstrate polyunsaturated fatty acid in order to convert said substrateto a product polyunsaturated fatty acid.
 15. The method according toclaim 14, wherein said substrate polyunsaturated fatty acid is DGLA or20-4:n-3 and said product polyunsaturated fatty acid is AA or EPA,respectively.
 16. The method according to claim 14 further comprisingthe step of exposing said product polyunsaturated fatty acid to anelongase in order to convert said product polyunsaturated fatty acid toanother polyunsaturated fatty acid.
 17. The method according to claim 16wherein said product polyunsaturated fatty acid is AA or EPA and saidanother polyunsaturated fatty acid is adrenic acid or(n-3)-docosapentaenoic acid, respectively.
 18. The method of claim 16further comprising the step of exposing said another polyunsaturatedfatty acid to an additional desaturase in order to convert said anotherpolyunsaturated fatty acid to a final polyunsaturated fatty acid. 19.The method of claim 17 wherein said final polyunsaturated fatty acid is(n-6)-docosapentaenoic acid or docosahexaenoic (DHA) acid.
 20. Anisolated nucleic acid sequence encoding a polypeptide having at least95% sequence identity to SEQ ID NO:20, wherein said nucleic acidsequence encodes a functionally active Δ5-desaturase.
 21. The isolatednucleic acid sequence of claim 20, wherein said Δ5-desaturase utilizes apolyunsaturated fatty acid as a substrate.
 22. The isolated nucleic acidsequence of claim 20, wherein said nucleic acid sequence is isolatedfrom Saprolegnia diclina.